Nephrology

Match each patient's clinical presentation with their most likely expected serum and urine laboratory profile.

A $45$-year-old man is brought to the emergency department by his sister due to altered mental status. She states that he has a history of alcohol use disorder and was found confused in his apartment with an empty bottle of antifreeze nearby. Laboratory studies show:

Based on these laboratory results, what is this patient's calculated osmolar gap? (Provide the exact numerical value)

A 74-year-old man is evaluated in the surgical telemetry unit on postoperative day 4 following an open cholecystectomy and common bile duct exploration. The nursing staff requested a review because his urine output has decreased to $250 \text{ mL}$ over the last 24 hours, and he has become increasingly confused and short of breath. His medical history includes hypertension, type 2 diabetes mellitus, and a 40-pack-year smoking history. Temperature is $37.6^\circ\text{C}$ ($99.7^\circ\text{F}$), blood pressure is $155/92 \text{ mm Hg}$, pulse is $112/\text{min}$, and respirations are $26/\text{min}$. Oxygen saturation is $88\%$ on room air. Physical examination shows jugular venous distention $10 \text{ cm}$ above the sternal angle. Auscultation of the lungs reveals bilateral basilar crackles. The abdomen is soft and non-tender, with intact surgical staples and no erythema. Bilateral $2+$ pitting edema is present in the lower extremities.

Laboratory studies show:
Serum sodium: $134 \text{ mEq/L}$
Serum potassium: $5.2 \text{ mEq/L}$
Serum chloride: $98 \text{ mEq/L}$
Serum bicarbonate: $14 \text{ mEq/L}$
Blood urea nitrogen: $68 \text{ mg/dL}$
Serum creatinine: $3.1 \text{ mg/dL}$ (baseline $1.1 \text{ mg/dL}$)

Arterial blood gas (room air):
pH: $7.24$
PaCO2: $42 \text{ mm Hg}$
PaO2: $58 \text{ mm Hg}$

Which of the following is the most accurate characterization of this patient's acid-base status and the most appropriate next step in management?

Emergency medical services bring a 68-year-old man to the hospital after his daughter found him lethargic and struggling to breathe. For the past 48 hours, he has experienced a fever and a worsening productive cough. His medical history is significant for severe chronic obstructive pulmonary disease (COPD), hypertension, and type 2 diabetes mellitus. His daily medications include tiotropium, lisinopril, and empagliflozin.

Vital signs are:
Temperature: 38.2°C (100.8°F)
Blood pressure: 110/65 mm Hg
Pulse: 118/min
Respirations: 26/min
Oxygen saturation: 86% on room air

Physical examination reveals a somnolent but arousable patient. Lung auscultation demonstrates diffuse wheezing and right lower lobe crackles with a prolonged expiratory phase.

Laboratory results are as follows:

Arterial blood gas analysis on room air reveals:

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

During morning rounds in the intensive care unit, the medical team evaluates a patient with septic shock secondary to a perforated viscus. The patient's arterial blood gas and basic metabolic panel are drawn to assess his acid-base status. The laboratory results reveal a severe primary metabolic acidosis with a serum bicarbonate level of $14 \text{ mEq/L}$ and a significantly elevated serum lactate. To determine if a superimposed respiratory acid-base disorder is present, the physician calculates the expected respiratory response. Assuming appropriate respiratory compensation, which of the following is the expected partial pressure of carbon dioxide ($PaCO_2$) in this patient?

An 82-year-old man with advanced Alzheimer dementia is brought to the emergency department from a skilled nursing facility due to progressive lethargy over the past 3 days. The facility staff report that he has been refusing meals and liquids. On examination, temperature is 37.1°C (98.8°F), blood pressure is 98/60 mm Hg, pulse is 112/min, and respiratory rate is 16/min. The patient appears cachectic with profoundly dry mucous membranes and poor skin turgor. His current weight is 60 kg (132 lb).

Laboratory studies show:
Serum sodium: 168 mEq/L
Serum potassium: 4.1 mEq/L
Serum chloride: 129 mEq/L
Serum bicarbonate: 24 mEq/L
Blood urea nitrogen: 56 mg/dL
Serum creatinine: 1.8 mg/dL

Based on an estimated total body water of 50% of his body weight, what is this patient's calculated free water deficit in liters?

Laboratory evaluation is performed during a routine follow-up visit for a 64-year-old man with a 15-year history of type 2 diabetes mellitus and hypertension. The patient reports feeling generally well and explicitly denies any recent nausea, vomiting, or diarrhea. His current medication regimen consists of metformin, lisinopril, amlodipine, and atorvastatin. Blood pressure is $134/82 \text{ mmHg}$ and pulse is $72/\text{min}$.

Laboratory results are as follows:

Urinalysis reveals a pH of $5.2$ and is negative for glucose, ketones, and cellular casts.

Which of the following pathophysiologic mechanisms best explains this patient's current laboratory findings?

A 72-year-old man is evaluated in the hospital for decreased urine output. He was admitted 3 days ago for an acute exacerbation of heart failure with reduced ejection fraction. His treatment regimen includes intravenous furosemide, lisinopril, carvedilol, and spironolactone. His weight has decreased by 4 kg (8.8 lb) since admission, and his peripheral edema has significantly improved. However, his urine output over the last 12 hours has been only 250 mL.

Vitals:
Blood pressure: 102/60 mm Hg
Heart rate: 94/min

Laboratory results from today:
Serum:
Sodium: 135 mEq/L
Potassium: 4.8 mEq/L
Chloride: 98 mEq/L
Bicarbonate: 28 mEq/L
Blood urea nitrogen: 80 mg/dL
Creatinine: 2.4 mg/dL

Urine:
Sodium: 75 mEq/L
Creatinine: 120 mg/dL
Urea nitrogen: 600 mg/dL

Based on the laboratory findings, what is this patient's calculated fractional excretion of urea (expressed as a percentage)?

Match the following glomerular diseases with their classic renal biopsy or immunofluorescence findings.

A 68-year-old man is brought to the emergency department with 3 days of severe, watery diarrhea and poor oral intake. He reports feeling lightheaded upon standing. His temperature is $37.1^\circ$ C ($98.8^\circ$ F), blood pressure is $112/72$ mm Hg supine and $90/60$ mm Hg standing, and pulse is 92/min supine and 116/min standing. Physical examination reveals dry mucous membranes and delayed capillary refill.

Laboratory results are as follows:

Serum studies:
Sodium: $140$ mEq/L
Potassium: $3.5$ mEq/L
Chloride: $110$ mEq/L
Bicarbonate: $20$ mEq/L
Blood urea nitrogen: $42$ mg/dL
Creatinine: $1.4$ mg/dL

Urine studies:
Sodium: $20$ mEq/L
Creatinine: $40$ mg/dL

Based on these findings, what is the patient's fractional excretion of sodium?

A 58-year-old male is evaluated in the emergency department after his family noted progressive lethargy and confusion. According to his wife, he has experienced severe, nonbloody, bilious vomiting for the past five days. He has been unable to tolerate oral intake and has had minimal urine output for the past 24 hours. His medical history includes hypertension and untreated peptic ulcer disease. On physical examination, blood pressure is $88/54 \text{ mm Hg}$, and pulse is $118/\text{min}$. The patient appears lethargic. Mucous membranes are extremely dry, and skin turgor is significantly decreased.

Laboratory studies show the following:
Sodium: $140 \text{ mEq/L}$
Potassium: $3.2 \text{ mEq/L}$
Chloride: $90 \text{ mEq/L}$
Bicarbonate: $25 \text{ mEq/L}$
Blood urea nitrogen: $72 \text{ mg/dL}$
Creatinine: $3.4 \text{ mg/dL}$
Lactate: $6.2 \text{ mmol/L}$

Arterial blood gas (room air):
pH: $7.37$
$pCO_2$: $45 \text{ mm Hg}$
$pO_2$: $88 \text{ mm Hg}$

Which of the following best describes this patient's underlying acid-base derangements?

A 50-year-old male presents to the outpatient clinic reporting progressive weakness and a metallic taste in his mouth over the last several weeks. He has a 15-year history of poorly controlled hypertension. His blood pressure is $165/95 \text{ mm Hg}$, pulse is $84/\text{min}$, and respiratory rate is $22/\text{min}$. Physical examination reveals trace bilateral lower extremity edema and a pale complexion. Laboratory studies are obtained and reveal the following:

Serum chemistry:
$Na^+$: $140 \text{ mEq/L}$
$K^+$: $5.2 \text{ mEq/L}$
$Cl^-$: $102 \text{ mEq/L}$
$HCO_3^-$: $12 \text{ mEq/L}$
Blood urea nitrogen: $85 \text{ mg/dL}$
Serum creatinine: $5.5 \text{ mg/dL}$

Arterial blood gas (room air):
pH: $7.25$
$pCO_2$: $26 \text{ mm Hg}$
$pO_2$: $95 \text{ mm Hg}$

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

Match each clinical presentation with the most likely corresponding serum and urine laboratory findings.

Match each patient's clinical presentation with the primary pathophysiologic mechanism or underlying diagnosis responsible for their electrolyte and acid-base disturbances.

An 18-year-old female gymnast is brought to the university health clinic by her roommate. She has been vomiting persistently for the past four days. The roommate mentions she has observed similar episodes in the past, though not this severe. Physical examination shows dry mucous membranes, poor skin turgor, and a pulse of 112/min.

Laboratory studies show the following:
- $Na^+$: 139 mEq/L
- $K^+$: 2.9 mEq/L
- $Cl^-$: 94 mEq/L
- $HCO_3^-$: 36 mEq/L

Arterial blood gas analysis on room air reveals:
- pH: 7.52
- $pCO_2$: 48 mm Hg
- $pO_2$: 94 mm Hg

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

Match the following classic urinalysis sediment findings with the most appropriate renal pathology or clinical syndrome.

Match the following diuretic medications with their primary site and mechanism of action within the nephron.

A 24-year-old woman with a history of type 1 diabetes mellitus presents to the emergency department with a 3-day history of intractable nausea, vomiting, and diffuse abdominal pain. She reports that her insulin pump malfunctioned four days ago. On physical examination, she appears lethargic and has dry mucous membranes. Her pulse is 118/min, blood pressure is 98/60 mm Hg, and respirations are 26/min and deep.

Laboratory studies show:
Serum:
Sodium: $140 \text{ mEq/L}$
Potassium: $4.8 \text{ mEq/L}$
Chloride: $88 \text{ mEq/L}$
Bicarbonate: $16 \text{ mEq/L}$
Blood urea nitrogen: $42 \text{ mg/dL}$
Creatinine: $1.6 \text{ mg/dL}$
Glucose: $520 \text{ mg/dL}$

Arterial blood gas (room air):
pH: 7.34
$\text{pCO}_2$: $31 \text{ mm Hg}$
$\text{pO}_2$: $95 \text{ mm Hg}$

Assume a normal serum anion gap of $12 \text{ mEq/L}$ and a normal serum bicarbonate of $24 \text{ mEq/L}$.

What is this patient's delta-delta ratio ($\frac{\Delta \text{AG}}{\Delta \text{HCO}_3^-}$)?

During a routine follow-up at the nephrology clinic, a 42-year-old woman is evaluated for persistent hypokalemia and mild muscle weakness. She has a history of Sjögren syndrome and has had two episodes of calcium phosphate nephrolithiasis in the past five years. She reports no diarrhea, vomiting, or recent dietary changes. Her blood pressure is 118/76 mm Hg. Laboratory studies show:

Serum sodium: 140 mEq/L
Serum potassium: 2.9 mEq/L
Serum chloride: 115 mEq/L
Serum bicarbonate: 15 mEq/L
Blood urea nitrogen: 12 mg/dL
Serum creatinine: 0.8 mg/dL

Urine studies obtained simultaneously show:
Urine sodium: 55 mEq/L
Urine potassium: 25 mEq/L
Urine chloride: 60 mEq/L

What is this patient's urine anion gap in mEq/L? (Provide your answer as a number only)

A 24-year-old man is brought to the emergency department by his roommate due to increasing lethargy and confusion over the past 12 hours. The patient has a history of type 1 diabetes mellitus and has not taken his insulin for the past week due to financial constraints. Vital signs show a temperature of $37.1^\circ$ C ($98.8^\circ$ F), heart rate of 115/min, blood pressure of 105/68 mm Hg, and a respiratory rate of 28/min with deep, rapid breaths.

Laboratory studies reveal:

Which of the following arterial $pCO_2$ values would best indicate an appropriate, isolated respiratory compensation for this patient's acid-base disturbance?