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Difficulty: MediumInterpreting Laboratory Results

A physician is reviewing laboratory results for four different patients in the emergency department. Match each patient's combined arterial blood gas (ABG) and basic metabolic panel (BMP) profile with the most likely clinical diagnosis. Assume a normal reference range for serum anion gap is 88-1212 mEq/L.

  • pH 7.227.22, pCO 2_2 6565 mmHg, HCO 3−_3^- 2626 mEq/L, Na +^+ 140140 mEq/L, Cl −^- 102102 mEq/LAcute opioid intoxication
  • pH 7.497.49, pCO 2_2 4848 mmHg, HCO 3−_3^- 3636 mEq/L, Na +^+ 138138 mEq/L, Cl −^- 9292 mEq/L, Urine Cl −^- <10< 10 mEq/LCovert bulimia nervosa
  • pH 7.287.28, pCO 2_2 2828 mmHg, HCO 3−_3^- 1313 mEq/L, Na +^+ 142142 mEq/L, Cl −^- 119119 mEq/LSevere infectious enteritis
  • pH 7.297.29, pCO 2_2 3030 mmHg, HCO 3−_3^- 1414 mEq/L, Na +^+ 140140 mEq/L, Cl −^- 104104 mEq/LDiabetic ketoacidosis

Answer

The correct pairings match the uncompensated respiratory acidosis to opioid intoxication; the chloride-responsive metabolic alkalosis to bulimia nervosa; the normal anion gap metabolic acidosis to infectious enteritis; and the high anion gap metabolic acidosis to diabetic ketoacidosis.
Each laboratory pattern reflects a distinct pathophysiologic state: hypoventilation causes an acute respiratory acidosis (opioids); vomiting causes a chloride-responsive metabolic alkalosis (bulimia); lower gastrointestinal bicarbonate loss causes a normal anion gap metabolic acidosis (enteritis); and organic acid accumulation causes a high anion gap metabolic acidosis (diabetic ketoacidosis).

Step-by-Step Solution

1
Analyze the primary acid-base disturbance for each laboratory profile using the pH, pCO2, and HCO3- values.
The first profile is an acute respiratory acidosis. The third and fourth profiles are metabolic acidoses. The second profile is a metabolic alkalosis.
Establishing the primary disorder (respiratory versus metabolic) narrows down the pathophysiologic mechanism immediately.
2
Calculate the serum anion gap (Na+−(Cl−+HCO3−)Na^+ - (Cl^- + HCO_3^-)) for the two metabolic acidosis profiles.
The third profile has an anion gap of 10 mEq/L (normal). The fourth profile has an anion gap of 22 mEq/L (elevated).
Categorizing metabolic acidosis into normal gap (NAGMA) versus high gap (HAGMA) is essential for identifying the specific underlying etiology.
3
Evaluate the additional urinary indices and clinical context for the metabolic alkalosis profile.
The second profile shows a metabolic alkalosis with a low urine chloride.
Urine chloride differentiates saline-responsive (e.g., vomiting, remote diuretic use) from saline-resistant (e.g., hyperaldosteronism) causes of metabolic alkalosis.

Key Concept

Acid-base disorders are identified by determining the primary disturbance (respiratory vs. metabolic), calculating the anion gap for any metabolic acidosis, and utilizing urine electrolytes when evaluating metabolic alkalosis.
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Interpreting Laboratory Results

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