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Question 1401Question →

Match each patient's clinical presentation with the most likely acid-base and electrolyte profile expected on their laboratory evaluation.

Click a left item, then click its matching right item

Items

A 22-year-old woman presenting with severe, recurrent vomiting due to hyperemesis gravidarum.
A 35-year-old man presenting with volume depletion following 5 days of profuse, watery diarrhea.
A 45-year-old man presenting with altered mental status and acute kidney injury following antifreeze ingestion.
A 28-year-old woman with Sjogren syndrome presenting with recurrent calcium phosphate nephrolithiasis and profound muscle weakness.

Matches

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Answer

The presentations match as follows: Hyperemesis with hypokalemic metabolic alkalosis; Diarrhea with normal anion gap acidosis and low urine pH; Ethylene glycol with high anion gap acidosis; and Type 1 RTA with normal anion gap acidosis and high urine pH.
Understanding the pathophysiology of fluid and electrolyte losses allows for accurate prediction of laboratory panels. Vomiting depletes HCl leading to alkalosis; lower GI losses deplete HCO3- leading to normal AG acidosis with appropriate compensation; toxic alcohols introduce unmeasured anions leading to high AG acidosis; and distal tubular defects prevent H+ secretion leading to normal AG acidosis with inappropriately alkaline urine.

Step-by-Step Solution

1
Determine the primary mechanism of acid-base disturbance for each clinical scenario.
Vomiting loses H+ and Cl-. Diarrhea loses HCO3- and K+. Antifreeze adds unmeasured toxic acids. Sjogren syndrome causes distal tubular dysfunction (Type 1 RTA).
Identifying the source of acid gain, acid loss, or bicarbonate loss is the first step in predicting the laboratory profile.
2
Correlate the mechanism with the specific anion gap status and compensatory urinary findings.
Vomiting causes hypochloremic alkalosis. Diarrhea causes normal AG acidosis with appropriate urine acidification. Antifreeze causes high AG acidosis. Type 1 RTA causes normal AG acidosis with failed urine acidification.
Distinguishing between different causes of normal gap acidosis requires evaluating the urinary pH and potassium levels.

Key Concept

Pathophysiology and differentiation of acid-base and electrolyte disturbances.
Question 1402Question →

A 68-year-old man is evaluated in the intensive care unit for altered mental status and respiratory distress. He was admitted 2 days ago for severe community-acquired pneumonia. He has a history of severe chronic obstructive pulmonary disease (COPD) with a baseline FEV1FEV_1 of 30% of predicted. Upon admission, he was started on intravenous ceftriaxone and azithromycin. Sputum cultures from admission are currently growing *Streptococcus pneumoniae* susceptible to ceftriaxone, and azithromycin has been discontinued. Over the last 3 hours, he has become increasingly lethargic and confused.

Temperature is 38.6°C (101.5°F), heart rate is 122/min, blood pressure is 84/52 mm Hg, and respiratory rate is 32/min. Oxygen saturation is 89% on 6 L/min via nasal cannula. The patient is diaphoretic with warm extremities. Lung auscultation reveals right lower lobe bronchial breath sounds and diffuse scattered expiratory wheezes. Cardiac examination reveals a regular tachycardia with no murmurs, rubs, or gallops. Jugular venous pressure is normal.

Laboratory results are as follows:
Leukocytes: 18,000/mm318,000/mm^3
Serum lactate: 6.26.2 mmol/L

Arterial blood gas (on 6 L/min O2O_2):
pH: 7.187.18
PaCO2PaCO_2: 3838 mm Hg
PaO2PaO_2: 5858 mm Hg
HCO3−HCO_3^-: 1414 mEq/L

Which of the following is the most appropriate next step in management?

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Answer: Endotracheal intubation and administration of intravenous crystalloid fluids

Answer

The most appropriate next step is to perform endotracheal intubation and administer intravenous crystalloid fluids.
The correct intervention is endotracheal intubation and intravenous crystalloid fluids. This patient with severe COPD and community-acquired pneumonia has developed septic shock, evidenced by hypotension, tachycardia, warm extremities, and an elevated lactate level. The arterial blood gas reveals a primary metabolic acidosis (pH 7.18, HCO3 14 mEq/L). Using Winter's formula, the expected PaCO2PaCO_2 is (1.5×14)+8=29±2(1.5 \times 14) + 8 = 29 \pm 2 mm Hg. The patient's actual PaCO2PaCO_2 is 38 mm Hg. Because the actual PaCO2PaCO_2 is significantly higher than the expected value, the patient has a concomitant respiratory acidosis. Although 38 mm Hg falls within the normal laboratory reference range, in the context of severe metabolic acidosis, it represents a failure of respiratory compensation due to severe respiratory muscle fatigue. Coupled with his lethargy and confusion, this indicates impending respiratory arrest. He requires immediate endotracheal intubation to secure the airway and decrease the work of breathing, alongside intravenous crystalloid fluids to restore intravascular volume in distributive shock.

Step-by-Step Solution

1
Analyze the primary acid-base disorder.
The arterial blood gas shows acidemia (pH 7.18) with a low HCO3−HCO_3^- (14 mEq/L), indicating a primary metabolic acidosis (driven by elevated lactate from septic shock).
Identifying the primary disorder is required before evaluating the adequacy of physiological compensation.
2
Calculate the expected respiratory compensation using Winter's formula.
Expected PaCO2=(1.5×14)+8=21+8=29±2PaCO_2 = (1.5 \times 14) + 8 = 21 + 8 = 29 \pm 2 mm Hg.
This determines if the patient's respiratory drive is appropriately compensating for the metabolic acidosis.
3
Compare the actual PaCO2PaCO_2 to the expected PaCO2PaCO_2.
The patient's actual PaCO2PaCO_2 is 38 mm Hg, which is significantly higher than the expected range of 27-31 mm Hg.
An actual PaCO2PaCO_2 higher than expected reveals a superimposed respiratory acidosis, indicating severe respiratory muscle fatigue.
4
Determine the necessary clinical intervention based on respiratory and hemodynamic status.
The patient has altered mental status, septic shock, and mixed acid-base failure, necessitating immediate invasive mechanical ventilation (intubation) and volume resuscitation (crystalloids).
Noninvasive ventilation is contraindicated due to lethargy (inability to protect the airway), and shock requires immediate preload support.

Key Concept

Diagnosis of mixed acid-base disorders using Winter's formula and recognition of impending respiratory failure in septic shock.
Question 1403Question →

A 54-year-old man with decompensated cirrhosis secondary to alcohol use disorder and chronic hepatitis C infection is admitted to the hospital with a 2-day history of increasing confusion and progressive abdominal distension. He has a known history of esophageal varices for which he takes nadolol. Other home medications include spironolactone and lactulose.

On physical examination, temperature is 37.9°C (100.2°F), pulse is 92/min, and blood pressure is 98/60 mmHg. He appears lethargic but arousable, and is oriented to person only. Asterixis is present. The abdomen is markedly distended and non-tender, with shifting dullness and a positive fluid wave. There is 2+ pitting edema of the lower extremities.

Laboratory TestResult
Hemoglobin10.1 g/dL10.1 \text{ g/dL}
Platelet count65,000/mm365,000/\text{mm}^3
Leukocyte count11,200/mm311,200/\text{mm}^3
Serum sodium130 mEq/L130 \text{ mEq/L}
Serum potassium3.9 mEq/L3.9 \text{ mEq/L}
Blood urea nitrogen45 mg/dL45 \text{ mg/dL}
Serum creatinine1.9 mg/dL1.9 \text{ mg/dL} (baseline 0.9 mg/dL0.9 \text{ mg/dL} two months ago)
Total bilirubin4.2 mg/dL4.2 \text{ mg/dL}
Albumin2.6 g/dL2.6 \text{ g/dL}
Prothrombin time, INR1.81.8

A diagnostic paracentesis yields cloudy yellow fluid. Ascitic fluid analysis shows:

Ascitic Fluid AnalysisResult
Total protein1.2 g/dL1.2 \text{ g/dL}
Albumin0.4 g/dL0.4 \text{ g/dL}
Leukocyte count850/mm3850/\text{mm}^3 (82%82\% neutrophils)
Gram stainNo organisms seen

The patient is started on intravenous cefotaxime. Which of the following is the most appropriate additional step in the management of this patient?

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Answer: Withhold spironolactone and nadolol, and administer intravenous albumin

Answer

Withhold spironolactone and nadolol, and administer intravenous albumin
The patient has spontaneous bacterial peritonitis (SBP) complicated by acute kidney injury (AKI). In patients with SBP, intravenous albumin is indicated to prevent hepatorenal syndrome (HRS) if they meet any of the following criteria: serum creatinine >1.0 mg/dL, blood urea nitrogen >30 mg/dL, or total bilirubin >4.0 mg/dL. This patient meets all three criteria, making albumin administration essential. Furthermore, when a cirrhotic patient develops AKI, all nephrotoxic and hypotensive medications must be stopped. Diuretics (such as spironolactone) must be withheld to prevent further intravascular volume depletion. Additionally, current guidelines mandate the discontinuation of non-selective beta-blockers (such as nadolol) in patients with cirrhosis who develop SBP, refractory ascites, or AKI. These medications limit the compensatory increase in cardiac output required to maintain renal perfusion, thereby increasing mortality in this specific clinical context.

Step-by-Step Solution

1
Diagnose the primary acute complication
The patient has Spontaneous Bacterial Peritonitis (SBP) based on an ascitic fluid absolute neutrophil count of 697/mm³ (850 × 0.82), which is greater than the diagnostic threshold of 250/mm³.
Identifying SBP directs immediate antibiotic therapy, which has already been initiated with cefotaxime.
2
Identify concurrent complications
The patient has Acute Kidney Injury (AKI) with a creatinine rise from 0.9 mg/dL to 1.9 mg/dL.
Cirrhotic patients with SBP are at high risk for developing Hepatorenal Syndrome (HRS), a form of functional AKI caused by splanchnic vasodilation and renal vasoconstriction.
3
Determine the indications for albumin therapy in SBP
The patient meets criteria for IV albumin because his creatinine is >1.0 mg/dL, BUN is >30 mg/dL, and bilirubin is >4.0 mg/dL.
Intravenous albumin (1.5 g/kg on day 1, 1.0 g/kg on day 3) significantly reduces the incidence of HRS and mortality in patients with SBP who have renal or hepatic impairment.
4
Review home medications for necessary adjustments in the setting of AKI
Spironolactone and nadolol must be discontinued.
Diuretics exacerbate hypovolemia and AKI. Non-selective beta-blockers (NSBBs) like nadolol reduce compensatory cardiac output and renal perfusion, worsening outcomes in patients with severe refractory ascites, SBP, or AKI.

Key Concept

In patients with spontaneous bacterial peritonitis complicated by acute kidney injury, management requires intravenous albumin to prevent hepatorenal syndrome, alongside the cessation of diuretics and non-selective beta-blockers to preserve renal perfusion.
Estimated Time:2m 0s
Question 1404Question →

A 54-year-old woman is brought to the emergency department due to 3 days of fever, worsening abdominal pain, and profound lethargy. She has a history of Crohn's disease and underwent an extensive ileal resection two years ago. For the past week, she has had severe, voluminous watery diarrhea and has been unable to tolerate oral fluids. Her temperature is 38.9°C (102.0°F), blood pressure is 86/50 mm Hg, pulse is 122/min, and respirations are 24/min. Physical examination shows dry mucous membranes, decreased skin turgor, and diffuse abdominal tenderness with guarding.

TestResult
Arterial blood gas (room air)
pH7.26
pCO2pCO_223 mm Hg
pO2pO_288 mm Hg
Serum chemistries
Sodium135 mEq/L
Potassium3.2 mEq/L
Chloride105 mEq/L
Bicarbonate10 mEq/L
Blood urea nitrogen42 mg/dL
Creatinine2.3 mg/dL
Lactate5.5 mmol/L

Which of the following best characterizes this patient's acid-base status?

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Answer: Mixed elevated anion gap and normal anion gap metabolic acidosis with appropriate respiratory compensation

Answer

Mixed elevated anion gap and normal anion gap metabolic acidosis with appropriate respiratory compensation
This patient presents in hypovolemic shock with a severe mixed acid-base derangement. First, calculate the anion gap (AG): Na+−(Cl−+HCO3−)=135−(105+10)=20 mEq/LNa^+ - (Cl^- + HCO_3^-) = 135 - (105 + 10) = 20 \text{ mEq/L}. An AG > 12 confirms a primary elevated anion gap metabolic acidosis (AGMA), which is driven here by lactic acidosis (lactate of 5.5 mmol/L) secondary to tissue hypoperfusion. Second, perform a delta gap calculation to evaluate for additional metabolic disorders. The excess AG is 20−12=820 - 12 = 8. In a pure AGMA, the bicarbonate level should drop by 1 mEq/L for every 1 mEq/L increase in the AG. Therefore, the expected HCO3−HCO_3^- is 24−8=16 mEq/L24 - 8 = 16 \text{ mEq/L}. Because the patient's measured HCO3−HCO_3^- (10 mEq/L) is significantly lower than the expected 16 mEq/L, there must be a concurrent process further depleting bicarbonate. This indicates an underlying normal anion gap metabolic acidosis (NAGMA), which aligns clinically with her severe, voluminous diarrhea and history of extensive ileal resection. Finally, calculate the expected respiratory compensation using Winter's formula: Expected pCO2=(1.5×measured HCO3−)+8±2=(1.5×10)+8±2=23±2 mm HgExpected\ pCO_2 = (1.5 \times measured\ HCO_3^-) + 8 \pm 2 = (1.5 \times 10) + 8 \pm 2 = 23 \pm 2 \text{ mm Hg}. The measured pCO2pCO_2 is exactly 23 mm Hg, indicating that her respiratory compensation is perfectly appropriate for her degree of acidemia.

Step-by-Step Solution

1
Calculate the Anion Gap (AG).
AG=Na+−(Cl−+HCO3−)=135−(105+10)=20 mEq/LAG = Na^+ - (Cl^- + HCO_3^-) = 135 - (105 + 10) = 20 \text{ mEq/L}.
An AG > 12 establishes the presence of a primary elevated anion gap metabolic acidosis (AGMA).
2
Calculate the Delta Gap to identify mixed metabolic disorders.
Excess AG = 20−12=8 mEq/L20 - 12 = 8 \text{ mEq/L}. Expected HCO3−=24−8=16 mEq/LHCO_3^- = 24 - 8 = 16 \text{ mEq/L}. Measured HCO3−HCO_3^- (10 mEq/L) is less than the expected HCO3−HCO_3^-.
Because the measured bicarbonate is significantly lower than the expected value for a pure AGMA, a concurrent normal anion gap metabolic acidosis (NAGMA) is also present.
3
Calculate expected respiratory compensation using Winter's formula.
Expected pCO2=(1.5×10)+8±2=23±2 mm HgpCO_2 = (1.5 \times 10) + 8 \pm 2 = 23 \pm 2 \text{ mm Hg}. The measured pCO2pCO_2 is exactly 23 mm Hg.
Since the measured pCO2pCO_2 falls exactly within the expected range, the respiratory response is appropriate, ruling out an independent respiratory disorder.

Key Concept

Interpretation of complex mixed acid-base disorders using the anion gap, delta-delta gap, and Winter's formula.
Question 1405Question →

A 32-year-old woman presents to the urgent care clinic with profound weakness and lightheadedness. She reports having large-volume, watery stools up to 8 times a day for the past 4 days after returning from a camping trip. She has not been able to tolerate oral intake due to nausea.

Vital signs show a temperature of 37.1°C (98.8°F), blood pressure of 98/60 mm Hg, pulse of 115/min, and respiratory rate of 22/min. Physical examination reveals dry mucous membranes, flat neck veins, and delayed capillary refill.

Laboratory testing reveals the following:

TestResult
Sodium136 mEq/L
Potassium3.1 mEq/L
Chloride111 mEq/L
Bicarbonate15 mEq/L
Blood urea nitrogen (BUN)30 mg/dL
Creatinine1.2 mg/dL
Arterial blood gas analysis on room air:
TestResult
pH7.26
pCO2pCO_230 mm Hg
pO2pO_295 mm Hg

Which of the following best describes this patient's current acid-base status?

Show answer & explanation

Answer: Normal anion gap metabolic acidosis with appropriate respiratory compensation

Answer

Normal anion gap metabolic acidosis with appropriate respiratory compensation
This patient has a history of severe diarrhea, which causes profound gastrointestinal loss of bicarbonate, leading to a metabolic acidosis. The step-wise evaluation of her acid-base status confirms this diagnosis:

1. Primary Disorder: The arterial pH is 7.26, indicating acidemia. The serum bicarbonate (HCO3−HCO_3^-) is appropriately decreased at 15 mEq/L, confirming a primary metabolic acidosis.

2. Anion Gap: The serum anion gap is calculated as Na+−(Cl−+HCO3−)Na^+ - (Cl^- + HCO_3^-). For this patient, the gap is 136−(111+15)=10136 - (111 + 15) = 10 mEq/L. Since normal is typically 8-12 mEq/L, she has a normal anion gap metabolic acidosis (NAGMA).

3. Compensation: To determine if her respiratory compensation is adequate, Winter's formula is used: Expected pCO2=(1.5×[HCO3−])+8±2pCO_2 = (1.5 \times [HCO_3^-]) + 8 \pm 2.
Expected pCO2=(1.5×15)+8±2=30.5±2pCO_2 = (1.5 \times 15) + 8 \pm 2 = 30.5 \pm 2 mm Hg.
Because her measured pCO2pCO_2 is exactly 30 mm Hg, her respiratory response falls perfectly within the expected range (28.5 to 32.5 mm Hg). Thus, she has appropriate respiratory compensation with no superimposed mixed acid-base disorders.

Step-by-Step Solution

1
Identify the primary acid-base disorder using the pH and standard laboratory values.
The pH is 7.26 (acidemia). The HCO3−HCO_3^- is low (15 mEq/L).
Matching the low pH with a low bicarbonate level confirms that the primary disturbance is a metabolic acidosis.
2
Calculate the serum anion gap to determine the etiology of the metabolic acidosis.
Anion Gap = Na+−(Cl−+HCO3−)Na^+ - (Cl^- + HCO_3^-) = 136−(111+15)=10136 - (111 + 15) = 10 mEq/L.
An anion gap of 10 mEq/L is within the normal range (8-12 mEq/L), indicating a normal anion gap metabolic acidosis (NAGMA), which is consistent with this patient's history of severe diarrhea.
3
Apply Winter's formula to determine if the respiratory compensation is appropriate.
Expected pCO2=(1.5×15)+8±2=22.5+8±2=30.5±2pCO_2 = (1.5 \times 15) + 8 \pm 2 = 22.5 + 8 \pm 2 = 30.5 \pm 2 mm Hg (range: 28.5 to 32.5 mm Hg).
Because the patient's measured pCO2pCO_2 (30 mm Hg) falls within this expected range, there is purely appropriate respiratory compensation without a superimposed respiratory disorder.

Key Concept

The step-wise approach to acid-base disorders requires identifying the primary disturbance via pH, calculating the anion gap for metabolic acidosis, and utilizing Winter's formula (Expected pCO2=1.5×[HCO3−]+8±2pCO_2 = 1.5 \times [HCO_3^-] + 8 \pm 2) to check for appropriate respiratory compensation.
Question 1406Question →

A 28-year-old man comes to the clinic reporting progressive fatigue, weight gain, and sluggishness over the past 8 months. His medical history is notable for childhood acute lymphoblastic leukemia, which was treated with chemotherapy and cranial irradiation at age 6. He takes no medications. His pulse is 56/min and blood pressure is 110/70 mm Hg. Physical examination shows dry skin and delayed relaxation of the deep tendon reflexes. Laboratory studies show:

TestResultReference Range
Thyroid-stimulating hormone (TSH)1.1 mU/L0.5-5.0 mU/L
Free thyroxine (T4)0.6 ng/dL0.9-1.7 ng/dL

Which of the following is the most likely diagnosis?

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Answer: Central hypothyroidism

Answer

Central hypothyroidism
The correct answer is central hypothyroidism. The patient's symptoms (fatigue, weight gain, sluggishness) and physical examination findings (bradycardia, delayed deep tendon reflexes, dry skin) are classic for hypothyroidism. The laboratory evaluation confirms a low free T4 level. However, the TSH is within the normal range, which is inappropriately low for the degree of hypothyroxinemia. In an intact hypothalamic-pituitary-thyroid axis, a low free T4 should trigger a significant increase in TSH production due to the loss of negative feedback. The failure to mount an elevated TSH response, especially in a patient with a known risk factor (history of cranial irradiation), strongly indicates a central (pituitary or hypothalamic) etiology.

Step-by-Step Solution

1
Analyze the patient's symptoms and physical exam findings.
Fatigue, weight gain, bradycardia, and delayed deep tendon reflexes indicate a hypothyroid clinical state.
Establishing the clinical state provides context for interpreting endocrine laboratory values.
2
Interpret the thyroid function tests.
Free T4 is frankly low (0.6 ng/dL) while TSH remains in the normal range (1.1 mU/L).
To determine the underlying etiology of the hypothyroidism.
3
Correlate the lab findings with the patient's medical history.
The combination of low free T4 and an inappropriately normal TSH in a patient with a history of cranial irradiation points to central (pituitary or hypothalamic) dysfunction.
A normal thyroid gland would mount a significantly elevated TSH response to a low T4 level. The lack of this response indicates a central defect.

Key Concept

Diagnosis of central hypothyroidism relies on identifying a low free T4 level accompanied by an inappropriately low or normal TSH level.
Question 1407Question →

A 58-year-old man is brought to the emergency department via ambulance after coughing up approximately 600 mL of bright red blood over the past hour. He has a history of treated pulmonary tuberculosis 10 years ago and currently smokes 1 pack of cigarettes daily. On arrival, he is in moderate respiratory distress. His temperature is 37.2°C (99.0°F), blood pressure is 95/60 mmHg, pulse is 118/min, and respiratory rate is 26/min. Pulse oximetry shows an oxygen saturation of 89% on room air. Auscultation reveals coarse crackles and decreased breath sounds exclusively over the right upper lung field. The patient continues to actively cough up large amounts of blood. Arrange the following steps in the most appropriate chronological order for the acute management of this patient's condition.

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Answer

The correct chronological order strictly prioritizes the ABCs of resuscitation: 1) Secure the airway and protect the healthy lung (right lung down), 2) Establish intravenous access for hemodynamic support, 3) Perform bronchoscopy for localization, and 4) Proceed to bronchial artery embolization for definitive hemostasis.
The correct sequence strictly follows the fundamental 'ABC' principles of resuscitation in critical care. In massive hemoptysis (defined as >600 mL/24 hr or any amount causing hemodynamic/respiratory compromise), the primary mechanism of death is asphyxiation from blood drowning the functional lung units. Therefore, the absolute first step is Airway and Breathing (A/B): securing the airway (often via intubation) and placing the patient in a lateral decubitus position with the bleeding lung down. In this patient, right-sided crackles and a history of tuberculosis indicate a right-sided source, so the right lung should be dependent (down). Step two addresses Circulation (C): the patient is borderline hypotensive and tachycardic, requiring immediate large-bore IV access and fluid resuscitation. Only after the ABCs are stabilized should the clinician move to step three: localization of the bleeding via bronchoscopy. Finally, step four involves definitive hemostasis via bronchial artery embolization.

Step-by-Step Solution

1
Prioritize Airway and Breathing (A and B).
Identify that massive hemoptysis immediately threatens the airway due to asphyxiation.
Blood filling the alveolar space prevents gas exchange. Securing the airway and using gravity (bleeding right lung down) protects the healthy left lung.
2
Prioritize Circulation (C).
Recognize the patient's hemodynamic instability.
Hypovolemia from massive blood loss must be corrected immediately after the airway is secured to prevent hypovolemic shock and cardiovascular collapse.
3
Proceed to Diagnostic Localization.
Select bronchoscopy as the next logical step.
Before definitive therapy can be applied, the exact anatomic source of bleeding must be identified, and the airways must be cleared of obscuring clots.
4
Apply Definitive Treatment.
Select bronchial artery embolization.
This is the primary definitive therapeutic intervention to stop the bleeding once the patient is physiologically stable and the source is known.

Key Concept

The primary cause of mortality in massive hemoptysis is asphyxiation, making airway protection and positioning (bleeding lung dependent) the most critical initial steps, followed strictly by hemodynamic stabilization, localization, and definitive hemostasis.
Question 1408Question →

A 5252-year-old male with resistant hypertension and unprovoked hypokalemia (serum K+K^+ 2.9 mEq/L2.9 \text{ mEq/L}) is evaluated for suspected primary hyperaldosteronism. His current daily medication regimen includes maximal doses of amlodipine, perindopril, and chlorthalidone. The clinical team is evaluating him for potential curative surgical intervention. Arrange the following steps in the correct chronological sequence for the definitive diagnostic and pre-operative workup of this condition.

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Answer

The correct diagnostic algorithm sequence is: 1) Medication washout, 2) PAC/PRA screening ratio, 3) Confirmatory saline infusion test, 4) Adrenal CT scan, 5) Adrenal venous sampling.
The diagnosis of primary hyperaldosteronism requires a strict, sequential algorithmic approach to avoid misdiagnosis and inappropriate surgery. First, interfering medications must be removed to ensure an accurate baseline. Next, the PAC/PRA ratio is used as a highly sensitive screen. If positive, a confirmatory suppression test (e.g., saline infusion) is required because the screening test lacks specificity. Once biochemically confirmed, anatomic localization with an adrenal CT is performed. Finally, because the patient is over 3535 years of age, anatomical imaging must be followed by functional localization using bilateral adrenal venous sampling to differentiate a unilateral aldosterone-producing adenoma from bilateral hyperplasia.

Step-by-Step Solution

1
Address interfering factors (Medication Washout).
Discontinuation of ACE inhibitors and diuretics, switching to alpha-blockers or non-dihydropyridine calcium channel blockers.
These medications independently alter renin and aldosterone secretion, which would invalidate subsequent biochemical screening.
2
Perform the initial biochemical screen (PAC/PRA Ratio).
Measurement of aldosterone and renin to calculate the ratio.
A ratio >20>20 with an aldosterone level >15 ng/dL>15 \text{ ng/dL} indicates probable autonomous aldosterone production.
3
Confirm autonomous hypersecretion (Confirmatory Test).
Administration of a saline infusion or oral sodium load.
Demonstrates that the aldosterone production cannot be suppressed by volume expansion, distinguishing true primary hyperaldosteronism from false-positives.
4
Perform initial anatomic localization (Adrenal CT).
High-resolution cross-sectional imaging of the adrenal glands.
Evaluates for large masses, bilateral hyperplasia, or potential adrenocortical carcinoma to guide the next invasive step.
5
Perform functional lateralization (Adrenal Venous Sampling).
Catheterization of both adrenal veins to measure aldosterone/cortisol ratios.
Essential in patients >35>35 years to ensure a visualized nodule is actually the source of hormone overproduction (avoiding inappropriate surgery for a non-functioning incidentaloma).

Key Concept

The precise, stepwise diagnostic algorithm for primary hyperaldosteronism (Conn syndrome).
Estimated Time:2m 0s
Question 1409Question →

A 78-year-old woman is brought to the primary care clinic for a routine wellness visit. Her daughter reports that the patient has been eating well, sleeping normally, and participating in her usual daily activities. Her medical history is notable for hypertension and mild Alzheimer dementia. The patient's cognitive function is at her usual baseline, and she has not experienced any recent falls, confusion, or behavioral changes. She denies dysuria, increased urinary frequency, or lower abdominal pain. Vital signs, including a temperature of 37.1∘C37.1^{\circ}\mathrm{C} (98.8∘F98.8^{\circ}\mathrm{F}), are within normal limits. A urinalysis is obtained as part of a general screening panel, which returns positive for leukocyte esterase and nitrites. A subsequent urine culture grows >105>10^5 colony-forming units/mL of Escherichia coli. Which of the following is the most appropriate next step in management?

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Answer: Reassurance and clinical observation

Answer

Reassurance and clinical observation is the correct management, as the patient has asymptomatic bacteriuria.
The correct answer emphasizes that asymptomatic bacteriuria is a common, benign finding in older adults. Because the patient is entirely asymptomatic and at her cognitive baseline, no treatment is indicated. Treating this condition is a classic example of poor antimicrobial stewardship.

Step-by-Step Solution

1
Evaluate the patient's symptoms and cognitive baseline.
The patient is at her baseline cognitive function, has no signs of delirium, and denies any localized urinary symptoms.
To differentiate between a true, symptomatic urinary tract infection (UTI) and asymptomatic bacteriuria.
2
Interpret the urinalysis and urine culture results in the context of the clinical presentation.
The patient has a positive urine culture without associated clinical symptoms of infection.
Positive cultures in asymptomatic elderly patients indicate benign colonization rather than an invasive infection.
3
Determine the indication for antimicrobial therapy based on current stewardship guidelines.
No antibiotics or further diagnostic tests are indicated.
Treating asymptomatic bacteriuria in the general older adult population does not improve clinical outcomes and needlessly exposes patients to adverse drug events.

Key Concept

Asymptomatic bacteriuria (ASB) in the elderly population represents benign colonization and should not be screened for or treated with antibiotics, even in the presence of positive urinalysis or culture results.
Estimated Time:45s
Question 1410Question →

A 54-year-old woman is hospitalized for induction chemotherapy for acute myeloid leukemia. Seven days after completing the regimen, she develops a fever of 38.7°C (101.7°F). Her absolute neutrophil count is 150/mm³. Blood and urine cultures are drawn, and she is started on empiric intravenous cefepime. Five days later, she continues to have daily fevers up to 38.9°C (102.0°F). She is hemodynamically stable. She has no new symptoms. Physical examination reveals a clean, non-tender central venous catheter insertion site. There are no skin rashes, oral ulcers, or abnormal breath sounds. Her absolute neutrophil count is now 80/mm³. Blood cultures drawn on the first day of fever and repeat cultures drawn 48 hours ago show no growth. A chest radiograph is unremarkable. Which of the following is the most appropriate next step in management?

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Answer: Add intravenous caspofungin

Answer

The most appropriate next step is to add an intravenous antifungal agent, such as caspofungin.
This patient has persistent febrile neutropenia. The standard initial management for high-risk patients with neutropenic fever (absolute neutrophil count less than 500/mm³) is empiric broad-spectrum antipseudomonal antibacterial therapy, such as cefepime. If a patient remains febrile after 4 to 7 days of appropriate broad-spectrum antibacterial therapy and has an expected duration of neutropenia greater than 7 days (which is typical following acute myeloid leukemia induction), there is a high risk of an occult invasive fungal infection, most commonly Candida or Aspergillus species. Therefore, the addition of empiric antifungal therapy, such as an echinocandin (e.g., caspofungin) or liposomal amphotericin B, is the most appropriate next step in management.

Step-by-Step Solution

1
Identify the patient's clinical state and current treatment.
The patient has high-risk febrile neutropenia and has been on empiric cefepime for 5 days without defervescence.
Establishing the duration of broad-spectrum antibiotic therapy is critical for determining the next step in algorithmic management.
2
Evaluate for specific indications for altering antibacterial therapy or removing devices.
The patient is hemodynamically stable, has a clean catheter site, and has negative cultures, ruling out the immediate need for vancomycin or catheter removal.
Guidelines recommend adding Gram-positive coverage (e.g., vancomycin) only if specific complications are present.
3
Apply the guideline for persistent febrile neutropenia.
Determine that empiric antifungal therapy must be added.
Patients who remain febrile after 4-7 days of broad-spectrum antibiotics with an expected prolonged neutropenia are at high risk for occult invasive fungal infections.

Key Concept

Empiric antifungal therapy should be added in high-risk patients with neutropenia who have persistent or recurrent fever after 4 to 7 days of broad-spectrum antibiotics and no identified source.
Question 1411Question →

Match each patient's clinical presentation of medication-associated acute kidney injury to the precise pathophysiological mechanism of their renal impairment.

Click a left item, then click its matching right item

Items

A 65-year-old man with heart failure with reduced ejection fraction is prescribed indomethacin for an acute gout flare. His serum creatinine rapidly increases. Urinalysis is bland, and the fractional excretion of sodium is 0.4%.
A 72-year-old man with diffuse atherosclerosis and bilateral abdominal bruits is started on lisinopril for hypertension. His serum creatinine rises by 45% over the next week. Urinalysis is unremarkable.
A 60-year-old woman treated with high-dose intravenous gentamicin for Gram-negative bacteremia develops progressive, non-oliguric acute kidney injury on day 7 of therapy. Urinalysis reveals coarse, muddy brown granular casts.
A 48-year-old man receiving intravenous acyclovir for herpes simplex encephalitis develops acute oliguria within 48 hours. Urinalysis reveals red blood cells and birefringent needle-shaped crystals.
A 58-year-old man treated with intravenous nafcillin for methicillin-susceptible Staphylococcus aureus bacteremia develops a maculopapular rash and rising creatinine. Urinalysis shows white blood cell casts.

Matches

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Answer

The correct pairings link NSAIDs to afferent vasoconstriction, ACE inhibitors to efferent vasodilation, aminoglycosides to direct proximal tubular toxicity, acyclovir to intratubular crystal precipitation, and nafcillin to delayed hypersensitivity tubulointerstitial inflammation.
Each presentation maps to a distinct mechanism of medication-induced acute kidney injury. NSAIDs (indomethacin) cause afferent arteriolar vasoconstriction. ACE inhibitors (lisinopril) cause efferent arteriolar vasodilation. Aminoglycosides (gentamicin) cause direct acute tubular necrosis. Intravenous acyclovir causes mechanical obstruction via crystal precipitation. Beta-lactams (nafcillin) trigger immune-mediated acute interstitial nephritis.

Step-by-Step Solution

1
Analyze the first presentation (indomethacin in heart failure).
Identified as a hemodynamically mediated prerenal acute kidney injury.
NSAIDs inhibit cyclooxygenase, decreasing vasodilatory prostaglandins and causing unopposed afferent arteriolar vasoconstriction.
2
Analyze the second presentation (lisinopril in diffuse atherosclerosis).
Identified as a hemodynamically mediated acute kidney injury from loss of efferent tone.
ACE inhibitors block angiotensin II production, causing efferent arteriolar vasodilation and a precipitous drop in glomerular filtration pressure in patients reliant on this mechanism.
3
Analyze the third presentation (gentamicin with muddy brown casts).
Identified as acute tubular necrosis (ATN).
Aminoglycosides accumulate in the proximal tubule, causing direct cytotoxicity, cellular necrosis, and sloughing into the tubular lumen.
4
Analyze the fourth presentation (intravenous acyclovir with oliguria).
Identified as crystal nephropathy.
Acyclovir can precipitate in the renal tubules (especially with volume depletion), leading to mechanical obstruction and characteristic needle-shaped crystals.
5
Analyze the fifth presentation (nafcillin with rash and WBC casts).
Identified as acute interstitial nephritis (AIN).
Beta-lactams frequently trigger a delayed, idiosyncratic hypersensitivity reaction leading to interstitial edema and inflammatory cell infiltration.

Key Concept

Medication-induced acute kidney injury occurs via distinct pathophysiological mechanisms, including altered glomerular hemodynamics (NSAIDs, ACE inhibitors), direct tubular toxicity (aminoglycosides), tubulointerstitial inflammation (beta-lactams), and intratubular obstruction (acyclovir).
Estimated Time:2m 30s
Question 1412Question →

A 68-year-old man is brought to the emergency department by his wife due to progressive confusion, severe fatigue, and diffuse lower back pain over the past week. His wife reports he has had significantly diminished urine output for the last 3 days. His medical history is notable for a 40-pack-year smoking history and chronic obstructive pulmonary disease (COPD).

Vital signs are temperature 37.1°C (98.8°F), blood pressure 100/60 mmHg, heart rate 105/min, and respiratory rate 26/min. Pulse oximetry is 94% on room air.

Physical examination reveals pale conjunctivae and extremely dry mucous membranes. Pulmonary auscultation reveals distant breath sounds with faint scattered wheezes. The lower lumbar spine is tender to palpation.

Laboratory results are as follows:

Laboratory TestResultReference Range
Hemoglobin7.8 g/dL13.5-17.5 g/dL
Leukocyte count6,500/mm³4,500-11,000/mm³
Platelet count145,000/mm³150,000-400,000/mm³
Calcium13.8 mg/dL8.5-10.5 mg/dL
Creatinine4.5 mg/dL0.6-1.2 mg/dL
Blood urea nitrogen55 mg/dL8-20 mg/dL
Total protein10.5 g/dL6.0-8.0 g/dL
Albumin3.5 g/dL3.5-5.0 g/dL
Thyroid-stimulating hormone (TSH)0.2 µU/mL0.4-4.0 µU/mL
Free thyroxine (T4)0.8 ng/dL0.9-1.7 ng/dL
Arterial blood gas on room air:
ParameterResult
pH7.25
pCO2pCO_235 mmHg
pO2pO_265 mmHg
HCO3−HCO_3^-15 mEq/L

Which of the following is the most appropriate next step in the management of this patient?

Show answer & explanation

Answer: Initiate aggressive intravenous hydration with 0.9% sodium chloride

Answer

Initiate aggressive intravenous hydration with 0.9% sodium chloride
This patient presents with the classic CRAB criteria for Multiple Myeloma (hyperCalcemia, Renal failure, Anemia, Bone pain). Furthermore, the substantial difference between total protein and albumin indicates a large gamma gap, typical of monoclonal gammopathy. He is presenting with an oncologic emergency: severe hypercalcemia of malignancy. Hypercalcemia induces a nephrogenic diabetes insipidus, leading to profound polyuria, dehydration, and a subsequent drop in glomerular filtration rate (GFR). This volume depletion worsens the acute kidney injury (often combined with light chain cast nephropathy in myeloma). The absolute most critical first step in management is aggressive intravenous hydration with isotonic saline (0.9% sodium chloride). Saline restores intravascular volume, increases GFR, and increases sodium delivery to the distal tubules, which inhibits calcium reabsorption and promotes calciuresis.

Step-by-Step Solution

1
Analyze the classic tetrad of symptoms and lab findings.
The patient exhibits hypercalcemia (13.8 mg/dL), renal failure (Cr 4.5 mg/dL), anemia (Hb 7.8 g/dL), and bone pain, satisfying the CRAB criteria for Multiple Myeloma. The elevated total protein with normal albumin creates a gamma gap of 7.0 g/dL, confirming a monoclonal gammopathy.
Identifying the underlying oncologic diagnosis is necessary to understand the etiology of the acute presentation.
2
Identify the primary life-threatening derangement.
The patient is profoundly volume depleted (hypotension, tachycardia, dry mucous membranes) secondary to hypercalcemia-induced nephrogenic diabetes insipidus, which is simultaneously worsening his cast nephropathy and acute kidney injury.
Severe symptomatic hypercalcemia of malignancy is an oncologic emergency.
3
Determine the most appropriate immediate medical intervention.
Aggressive volume resuscitation with 0.9% sodium chloride (normal saline) is required to restore intravascular volume, improve the glomerular filtration rate (GFR), and promote the renal excretion of calcium.
Intravenous isotonic fluid is universally the first and most critical step in managing severe hypercalcemia, prior to administering targeted therapies like bisphosphonates or calcitonin.

Key Concept

The initial management of hypercalcemia of malignancy, particularly in the setting of Multiple Myeloma and acute kidney injury, is aggressive intravenous hydration with isotonic saline to restore intravascular volume and promote renal calcium excretion.
Question 1413Question →

A 24-year-old woman presents to the outpatient clinic with a 2-day history of painful urination and increased urinary frequency. She reports no fever, chills, nausea, vomiting, vaginal discharge, or back pain. She is otherwise healthy, has no known drug allergies, and takes no medications. Vital signs are within normal limits. Physical examination reveals mild suprapubic tenderness but is negative for costovertebral angle tenderness. A urine dipstick test is positive for leukocyte esterase and nitrites. Which of the following is the most appropriate empiric pharmacotherapy for this patient?

Show answer & explanation

Answer: Nitrofurantoin

Answer

Nitrofurantoin
The patient presents with classic symptoms and signs of uncomplicated acute cystitis (dysuria, frequency, suprapubic tenderness) without systemic involvement. Current guidelines recommend nitrofurantoin, trimethoprim-sulfamethoxazole, or fosfomycin as first-line empiric agents. Nitrofurantoin is highly concentrated in the urine, highly effective against typical uropathogens like Escherichia coli, and has a low impact on normal gastrointestinal flora, making it an excellent choice for antimicrobial stewardship.

Step-by-Step Solution

1
Analyze the patient's symptoms and examination findings.
The patient has dysuria, urinary frequency, and suprapubic pain without systemic signs (no fever) or upper urinary tract signs (no costovertebral angle tenderness).
To differentiate between uncomplicated cystitis and complicated infections like pyelonephritis.
2
Interpret the laboratory findings.
Positive leukocyte esterase and nitrites on urine dipstick strongly support a bacterial urinary tract infection.
To confirm the clinical suspicion of a bacterial etiology.
3
Select the most appropriate empiric treatment based on current guidelines.
Nitrofurantoin is chosen as a first-line oral agent for uncomplicated cystitis.
It provides targeted therapy for common uropathogens with a low risk of collateral damage and resistance compared to broad-spectrum options.

Key Concept

The first-line empiric treatments for uncomplicated acute cystitis in women include nitrofurantoin, trimethoprim-sulfamethoxazole, and fosfomycin, avoiding broad-spectrum agents to practice good antimicrobial stewardship.
Question 1414Question →

A 32-year-old woman comes to the clinic for evaluation of progressive fatigue, generalized weakness, and cold intolerance that has worsened over the past 4 months. She also reports that her menstrual periods, which were previously regular, have been absent for the past 6 months. She has no significant past medical history and takes no medications. Vital signs show a blood pressure of 100/65 mm Hg and a pulse of 52/min. Physical examination reveals dry skin and a delayed relaxation phase of the deep tendon reflexes. The thyroid gland is not palpable. Laboratory testing is obtained and reveals the following:

Laboratory TestResultReference Range
Thyroid-stimulating hormone (TSH)1.1 mU/L0.5–5.0 mU/L
Free thyroxine (T4)0.4 ng/dL0.9–1.7 ng/dL

Which of the following is the most likely underlying cause of this patient's clinical presentation?

Show answer & explanation

Answer: Decreased anterior pituitary secretion of thyrotropin

Answer

The most likely cause of this patient's presentation is a decrease in anterior pituitary secretion of thyrotropin, indicating central hypothyroidism.
The correct answer identifies that the patient has central (secondary) hypothyroidism. The patient presents with classic symptoms of a hypothyroid state, including profound fatigue, cold intolerance, bradycardia, and delayed deep tendon reflexes. Her laboratory results show a markedly low free T4 level. In primary hypothyroidism (where the thyroid gland itself fails), the anterior pituitary would respond to this low T4 by secreting high amounts of TSH. Because this patient's TSH is inappropriately normal, the defect lies in the anterior pituitary gland failing to secrete adequate thyrotropin (TSH). A common cause for this in young women is a pituitary adenoma, which can also disrupt the secretion of gonadotropins or increase prolactin, explaining her 6-month history of amenorrhea.

Step-by-Step Solution

1
Evaluate the clinical presentation and vital signs.
The patient exhibits bradycardia, delayed deep tendon reflexes, cold intolerance, fatigue, and amenorrhea.
Recognizing these classic signs and symptoms establishes a high clinical suspicion for a hypothyroid state.
2
Interpret the laboratory findings.
The free T4 level is low, but the TSH level is within the normal reference range.
In a properly functioning hypothalamic-pituitary-thyroid axis, a low free T4 should trigger a compensatory elevation in TSH. An inappropriately normal TSH indicates a failure of central regulation.
3
Synthesize clinical and laboratory data to determine the etiology.
The combination of hypothyroidism symptoms and an inappropriately normal TSH points to central (secondary) hypothyroidism, often due to a pituitary mass.
A pituitary lesion impairs the secretion of TSH (causing central hypothyroidism) and can also disrupt other pituitary hormones, explaining the patient's secondary amenorrhea.

Key Concept

Central (secondary) hypothyroidism is characterized by clinical features of hypothyroidism accompanied by a low free T4 and an inappropriately normal or low TSH level.
Question 1415Question →

Match each cardiovascular condition with its characteristic hemodynamic profile obtained during right heart catheterization.

Click a left item, then click its matching right item

Items

Cardiac tamponade
Constrictive pericarditis
Restrictive cardiomyopathy
Severe tricuspid regurgitation
Right ventricular infarction

Matches

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Answer

Cardiac tamponade corresponds to equalization of diastolic pressures and a blunted y descent. Constrictive pericarditis corresponds to discordant ventricular pressure changes and prominent x/y descents. Restrictive cardiomyopathy corresponds to concordant ventricular pressure changes and prominent x/y descents. Severe tricuspid regurgitation corresponds to a prominent systolic c-v wave and steep y descent. Right ventricular infarction corresponds to right atrial pressure equal to or greater than PCWP with normal pulmonary artery pressures.
Each specific cardiovascular condition generates a distinct hemodynamic signature driven by its pathophysiology. Tamponade restricts early diastolic filling, abolishing the y descent. Constriction limits mid-to-late filling and exhibits ventricular interdependence (discordance). Restriction mimics constriction but lacks interdependence (concordance). Tricuspid regurgitation introduces systolic atrial filling (c-v wave). RV infarction creates isolated right-sided pressure elevation without pulmonary hypertension.

Step-by-Step Solution

1
Identify the hemodynamic hallmark of cardiac tamponade.
Matched with absent or blunted y descent and equalization of diastolic pressures.
Pericardial fluid prevents early diastolic filling of the right ventricle, abolishing the normal y descent.
2
Differentiate between constrictive pericarditis and restrictive cardiomyopathy.
Constrictive pericarditis exhibits discordant respiratory changes, whereas restrictive cardiomyopathy exhibits concordant changes.
A thickened pericardium physically couples the ventricles, causing ventricular interdependence (discordance), which is absent when the pathology is isolated to the myocardium (concordance).
3
Analyze the right atrial tracing for severe tricuspid regurgitation.
Matched with the prominent c-v wave and rapid y descent.
Systolic regurgitant flow into the right atrium fuses the c and v waves; the engorged atrium then empties very rapidly in diastole.
4
Evaluate the hemodynamics of right ventricular infarction.
Matched with elevated right atrial pressure ≥ PCWP and normal pulmonary artery pressures.
The infarcted right ventricle serves as a passive conduit, leading to systemic venous congestion (high RA pressure) without adequate forward output to elevate left-sided or pulmonary pressures.

Key Concept

Hemodynamic differentiation of right-sided heart failure and pericardial diseases via right heart catheterization
Estimated Time:2m 0s
Question 1416Question →

Match each of the following hospital-acquired pathogen profiles with the most appropriate targeted antimicrobial therapy. Assume the patient has no reported drug allergies and normal renal function.

Click a left item, then click its matching right item

Items

Bloodstream infection with Escherichia coli demonstrating resistance to ceftriaxone but in vitro susceptibility to piperacillin-tazobactam
Bloodstream infection with Enterobacter cloacae demonstrating initial in vitro susceptibility to ceftriaxone, ceftazidime, and cefepime
Ventilator-associated pneumonia with Acinetobacter baumannii demonstrating broad resistance to antipseudomonal penicillins and carbapenems
Hospital-acquired pneumonia with Stenotrophomonas maltophilia

Matches

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Answer

Escherichia coli (ESBL) pairs with Meropenem; Enterobacter cloacae pairs with Cefepime; Acinetobacter baumannii pairs with Ampicillin-sulbactam; Stenotrophomonas maltophilia pairs with Trimethoprim-sulfamethoxazole.
Each pathogen requires specific stewardship knowledge: Meropenem is necessary for ESBL Enterobacterales due to proven mortality benefits; Cefepime resists AmpC beta-lactamase hydrolysis making it ideal for Enterobacter; Ampicillin-sulbactam works against Acinetobacter because sulbactam directly binds to penicillin-binding proteins of this specific organism; and Trimethoprim-sulfamethoxazole bypasses the intrinsic carbapenemases produced by Stenotrophomonas.

Step-by-Step Solution

1
Identify the resistance phenotype of the Escherichia coli isolate.
Recognized as an ESBL producer based on ceftriaxone resistance.
Requires carbapenem therapy (Meropenem) for invasive disease to reduce mortality, overriding in vitro susceptibility to piperacillin-tazobactam.
2
Evaluate the resistance risk for the Enterobacter cloacae isolate.
Recognized as a high-risk AmpC-producing organism.
Requires an AmpC-stable cephalosporin (Cefepime) or a carbapenem; ceftriaxone must be avoided due to the risk of rapid resistance induction.
3
Determine the optimal agent for carbapenem-resistant Acinetobacter baumannii.
Selected Ampicillin-sulbactam.
Sulbactam provides specific bactericidal activity against Acinetobacter, acting as the primary therapeutic component rather than just a beta-lactamase inhibitor.
4
Identify the first-line therapy for Stenotrophomonas maltophilia.
Selected Trimethoprim-sulfamethoxazole.
This organism is intrinsically resistant to carbapenems via chromosomal metallo-beta-lactamases, making Trimethoprim-sulfamethoxazole the drug of choice.

Key Concept

Antimicrobial stewardship and targeted therapy selection for multidrug-resistant nosocomial pathogens (ESBL, AmpC, CRAB, and Stenotrophomonas).
Estimated Time:1m 30s
Question 1417Question →

Match each clinical and laboratory profile describing a disturbance in calcium and phosphorus metabolism to its most likely underlying pathophysiologic mechanism or genetic etiology.

Click a left item, then click its matching right item

Items

A 1414-year-old girl with intellectual disability, obesity, shortened fourth and fifth metacarpals, serum calcium 7.27.2 mg/dL, phosphorus 6.56.5 mg/dL, and intact PTH 150150 pg/mL.
A 5252-year-old man with severe generalized bone pain, serum calcium 9.09.0 mg/dL, phosphorus 1.61.6 mg/dL, intact PTH 4545 pg/mL, and profoundly elevated plasma fibroblast growth factor 23 (FGF23).
A 4545-year-old woman with recurrent mucocutaneous candidiasis, muscle cramps, positive Chvostek sign, serum calcium 6.86.8 mg/dL, phosphorus 6.26.2 mg/dL, and intact PTH 88 pg/mL.
A 6565-year-old housebound man with proximal muscle weakness, waddling gait, serum calcium 7.87.8 mg/dL, phosphorus 2.22.2 mg/dL, intact PTH 120120 pg/mL, and alkaline phosphatase 350350 U/L.

Matches

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Answer

The correct pairings identify Pseudohypoparathyroidism type 1a (maternal GNAS1 mutation), Tumor-induced osteomalacia (mesenchymal neoplasm), Autoimmune Polyendocrine Syndrome Type 1 (AIRE gene mutation), and osteomalacia (nutritional vitamin D deficiency).
Each clinical scenario uniquely maps to a distinct pathophysiological disturbance of the bone-mineral axis. Precise interpretation of the PTH response relative to ambient calcium and phosphorus levels dictates the correct etiology.

Step-by-Step Solution

1
Analyze the first patient's laboratory profile and physical findings.
Hypocalcemia, hyperphosphatemia, and elevated PTH indicate end-organ PTH resistance. The physical features (obesity, shortened metacarpals) represent Albright hereditary osteodystrophy.
Recognizing the combination of PTH resistance and skeletal anomalies isolates the diagnosis to Pseudohypoparathyroidism type 1a (GNAS1 mutation).
2
Analyze the second patient's isolated laboratory abnormalities.
Profound hypophosphatemia with normal calcium and normal PTH, combined with high FGF23, indicates renal phosphate wasting.
In adults, acquired FGF23 excess is almost exclusively caused by paraneoplastic secretion from a benign phosphaturic mesenchymal tumor (tumor-induced osteomalacia).
3
Evaluate the third patient's endocrine and infectious manifestations.
Inappropriately low PTH in the setting of hypocalcemia and hyperphosphatemia confirms primary hypoparathyroidism. The concurrent candidiasis points to a polyendocrine syndrome.
The triad of primary hypoparathyroidism, chronic mucocutaneous candidiasis, and primary adrenal insufficiency defines APS-1, which is mediated by AIRE gene mutations.
4
Assess the fourth patient's presentation of weakness and specific bone markers.
Hypocalcemia combined with hypophosphatemia, elevated PTH, and elevated alkaline phosphatase indicates secondary hyperparathyroidism due to poor substrate availability.
Being housebound restricts sunlight exposure, leading to nutritional vitamin D deficiency. This impairs calcium and phosphorus absorption, triggering a compensatory, but ultimately maladaptive, PTH surge.

Key Concept

The differential diagnosis of complex calcium and phosphorus metabolic disorders relies on interpreting the directional changes of calcium, phosphorus, and PTH, combined with unique clinical phenotypes and genetic mechanisms.
Estimated Time:2m 0s
Question 1418Question →

A 45-year-old man is brought to the emergency department by paramedics after being found unresponsive in a park. His medical history is significant for severe alcohol use disorder. On physical examination, he is unarousable and his breath has a fruity odor. Temperature is 36.1°C (97.0°F), blood pressure is 105/65 mmHg, pulse is 102/min, and respiratory rate is 8/min and shallow. Pulse oximetry shows 92% on room air.

Laboratory results are as follows:
Serum sodium: 142 mEq/L
Serum potassium: 4.2 mEq/L
Serum chloride: 98 mEq/L
Serum bicarbonate: 14 mEq/L
Blood urea nitrogen: 28 mg/dL
Serum creatinine: 1.5 mg/dL

Arterial blood gas analysis on room air:
pH: 7.12
PaCO2PaCO_2: 45 mmHg
PaO2PaO_2: 65 mmHg

Which of the following describes the most accurate interpretation of this patient's acid-base status?

Show answer & explanation

Answer: High anion gap metabolic acidosis and concurrent primary respiratory acidosis

Answer

High anion gap metabolic acidosis and concurrent primary respiratory acidosis
The patient presents with acidemia (pH 7.12) and a low serum bicarbonate (14 mEq/L), indicating a metabolic acidosis. To correctly interpret the acid-base status, two main steps are required. First, the anion gap (AG) is calculated: AG=Na+−(Cl−+HCO3−)=142−(98+14)=30AG = Na^+ - (Cl^- + HCO_3^-) = 142 - (98 + 14) = 30 mEq/L. A normal AG is typically 8-12 mEq/L; therefore, the patient has a high anion gap metabolic acidosis, likely secondary to alcoholic ketoacidosis given his history. Next, Winter's formula must be applied to determine if the respiratory compensation is adequate: Expected PaCO2=(1.5×HCO3−)+8±2PaCO_2 = (1.5 \times HCO_3^-) + 8 \pm 2. Using the patient's bicarbonate of 14 mEq/L, the expected PaCO2PaCO_2 is 29±229 \pm 2 mmHg (range 27-31 mmHg). The patient's actual PaCO2PaCO_2 is 45 mmHg. Because the actual PaCO2PaCO_2 is significantly higher than expected, there is inadequate respiratory compensation, which constitutes a concurrent primary respiratory acidosis. This is clinically consistent with his central nervous system depression and hypoventilation (respiratory rate of 8/min) due to severe alcohol intoxication. Therefore, the correct interpretation is a high anion gap metabolic acidosis with a concurrent primary respiratory acidosis.

Step-by-Step Solution

1
Calculate the serum anion gap.
AG=Na+−(Cl−+HCO3−)=142−(98+14)=30AG = Na^+ - (Cl^- + HCO_3^-) = 142 - (98 + 14) = 30 mEq/L.
To determine the primary etiology of the metabolic acidosis. A normal AG is typically 8-12 mEq/L. Since 30 > 12, there is a primary high anion gap metabolic acidosis (HAGMA).
2
Calculate the expected PaCO2PaCO_2 using Winter's formula.
Expected PaCO2=(1.5×HCO3−)+8±2PaCO_2 = (1.5 \times HCO_3^-) + 8 \pm 2. Using a bicarbonate of 14 mEq/L, the expected PaCO2=(1.5×14)+8±2=29±2PaCO_2 = (1.5 \times 14) + 8 \pm 2 = 29 \pm 2 mmHg (range 27-31 mmHg).
To evaluate whether the respiratory compensation for the metabolic acidosis is adequate or if there is a secondary respiratory acid-base disorder.
3
Compare the expected PaCO2PaCO_2 with the measured PaCO2PaCO_2.
The measured PaCO2PaCO_2 of 45 mmHg is greater than the expected compensatory range of 27-31 mmHg.
A measured PaCO2PaCO_2 higher than expected indicates inadequate respiratory compensation, defining a concurrent primary respiratory acidosis (hypoventilation).

Key Concept

Diagnosis of mixed acid-base disorders using the anion gap and Winter's formula
Question 1419Question →

A 44-year-old man comes to the clinic reporting severe, episodic headaches accompanied by profuse sweating and a racing heart. These episodes occur 2 to 3 times a week and last for approximately 15 minutes. During an episode in the clinic, his blood pressure is 185/110 mm Hg and his heart rate is 115/min. Between episodes, he feels well and his vital signs are within normal limits. The physician suspects a catecholamine-secreting tumor. Arrange the following steps in the most appropriate chronological sequence for the evaluation and definitive management of this patient.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequence is: Biochemical confirmation (metanephrines), Anatomic localization (CT/MRI), Alpha-adrenergic blockade, Beta-adrenergic blockade, and finally Surgical resection.
The correct management of a suspected pheochromocytoma begins with biochemical confirmation of catecholamine excess using plasma or urine metanephrines. Once confirmed, abdominal imaging (CT or MRI) is performed to localize the tumor. Preoperative preparation requires a strict sequence of medical blockade to prevent intraoperative hypertensive crisis. Alpha-adrenergic blockade (e.g., phenoxybenzamine) is always initiated first to control blood pressure and allow volume expansion. Only after adequate alpha-blockade is achieved should beta-adrenergic blockade (e.g., propranolol) be added to control tachycardia. Finally, once the patient is medically optimized, surgical adrenalectomy is safely performed.

Step-by-Step Solution

1
Confirm diagnosis biochemically.
Metanephrines are measured.
Biochemical evidence of excess catecholamines is required before localizing a tumor to avoid working up benign incidentalomas.
2
Localize the tumor.
CT or MRI of the abdomen is performed.
To identify the exact anatomic location of the pheochromocytoma for surgical planning.
3
Administer alpha-blockers.
Vasodilation is achieved and blood pressure is controlled.
To prevent intraoperative hypertensive crisis and allow volume expansion.
4
Administer beta-blockers.
Heart rate is controlled.
To prevent tachycardia; this must be given strictly after alpha-blockers to avoid unopposed alpha-mediated vasoconstriction.
5
Perform surgical removal.
Adrenalectomy is completed.
To provide definitive cure of the tumor once the patient is medically optimized.

Key Concept

Diagnostic and Preoperative Management Sequence for Pheochromocytoma
Question 1420Question →

A 21-year-old woman is brought to the emergency department by her roommates due to confusion, rapid breathing, and excessive sweating. Her roommates report that she was studying for final exams and seemed highly stressed over the past few days. Upon arrival, the patient complains of a persistent ringing in her ears and nausea. Her temperature is 38.3°C (100.9°F), blood pressure is 110/70 mm Hg, pulse is 118/min, and respirations are 28/min. Physical examination reveals a diaphoretic, agitated patient with clear lungs and a regular heart rhythm.

Laboratory studies show the following:

Serum ChemistryResult
Sodium142 mEq/L
Potassium3.8 mEq/L
Chloride106 mEq/L
Bicarbonate16 mEq/L
Blood Urea Nitrogen (BUN)14 mg/dL
Creatinine0.9 mg/dL
Glucose98 mg/dL
Arterial Blood Gas (Room Air)Result
pH7.47
PaCO2PaCO_223 mm Hg
PaO2PaO_298 mm Hg

Based on these findings, which of the following best describes this patient's acid-base status?

Show answer & explanation

Answer: Mixed primary high anion gap metabolic acidosis and primary respiratory alkalosis

Answer

Mixed primary high anion gap metabolic acidosis and primary respiratory alkalosis
This patient's clinical presentation of tinnitus, hyperventilation, fever, and altered mental status is highly suggestive of salicylate toxicity. The acid-base analysis confirms this. Step 1: The pH of 7.47 indicates alkalemia. Step 2: The low PaCO2PaCO_2 of 23 mm Hg indicates a primary respiratory alkalosis. Step 3: Calculation of the anion gap [142 - (106 + 16) = 20 mEq/L] reveals a concurrent high anion gap metabolic acidosis. Step 4: Applying Winter's formula [1.5×16+8=32±21.5 \times 16 + 8 = 32 \pm 2 mm Hg] shows that the actual PaCO2PaCO_2 (23 mm Hg) is much lower than the expected compensatory response (30-34 mm Hg). Because the actual PaCO2PaCO_2 is lower than expected, an independent primary respiratory alkalosis is confirmed alongside the primary high anion gap metabolic acidosis.

Step-by-Step Solution

1
Evaluate the patient's primary acid-base status using pH.
The pH is 7.47, indicating alkalemia.
Determining the direction of the pH shift identifies the predominant primary acid-base disorder (in this case, an alkalosis).
2
Identify the primary driver of the alkalemia.
The PaCO2PaCO_2 is low (23 mm Hg), which aligns with the alkalemia. Therefore, a primary respiratory alkalosis is present.
A primary respiratory disorder is characterized by a PaCO2PaCO_2 shift that correlates with the pH shift.
3
Calculate the serum Anion Gap (AG) to screen for hidden metabolic disorders.
AG=Na+−(Cl−+HCO3−)=142−(106+16)=20AG = Na^+ - (Cl^- + HCO_3^-) = 142 - (106 + 16) = 20 mEq/L.
The normal AG is 8-12 mEq/L. An AG of 20 mEq/L definitively indicates the presence of a primary high anion gap metabolic acidosis, regardless of the overall pH.
4
Apply Winter's formula to determine if the PaCO2PaCO_2 is appropriately compensated for the metabolic acidosis.
Expected PaCO2=(1.5×HCO3−)+8±2Expected\ PaCO_2 = (1.5 \times HCO_3^-) + 8 \pm 2
Expected PaCO2=(1.5×16)+8=32±2 mm HgExpected\ PaCO_2 = (1.5 \times 16) + 8 = 32 \pm 2\ mm\ Hg
Comparing the expected PaCO2PaCO_2 (30-34 mm Hg) to the actual PaCO2PaCO_2 (23 mm Hg) shows that the actual value is significantly lower. This proves the respiratory alkalosis is an independent primary disorder, not just compensation.
5
Synthesize the findings with the clinical presentation.
The patient has a mixed primary high anion gap metabolic acidosis and primary respiratory alkalosis, classic for salicylate (aspirin) toxicity.
Salicylates directly stimulate the medullary respiratory center (causing respiratory alkalosis) and uncouple oxidative phosphorylation (causing lactic acidosis and ketoacidosis, resulting in HAGMA).

Key Concept

Salicylate toxicity classically presents with a mixed primary high anion gap metabolic acidosis and primary respiratory alkalosis, requiring calculation of both the anion gap and Winter's formula for accurate diagnosis.
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