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Difficulty: Very hardInterpreting Laboratory Results

A physician is evaluating five patients who present with complex acid-base and electrolyte abnormalities. Match each patient's clinical and laboratory profile to the most likely underlying diagnosis. All serum electrolytes are reported in mEq/L. The reference range for serum anion gap is 8−128-12 mEq/L.

  • Patient A: pH 7.257.25, PaCO 2_2 3030 mmHg, Na +^+ 140140 mEq/L, K +^+ 2.12.1 mEq/L, Cl −^- 115115 mEq/L, HCO 3−_3^- 1313 mEq/L, Urine pH 6.86.8, Urine AG positive, BP 120/80120/80 mmHgDistal (Type 11) renal tubular acidosis
  • Patient B: pH 7.307.30, PaCO 2_2 3636 mmHg, Na +^+ 139139 mEq/L, K +^+ 5.85.8 mEq/L, Cl −^- 110110 mEq/L, HCO 3−_3^- 1717 mEq/L, Urine pH 5.25.2, Urine AG positive, BP 130/85130/85 mmHgHyporeninemic hypoaldosteronism (Type 44 RTA)
  • Patient C: pH 7.527.52, PaCO 2_2 4848 mmHg, Na +^+ 136136 mEq/L, K +^+ 2.62.6 mEq/L, Cl −^- 8686 mEq/L, HCO 3−_3^- 3838 mEq/L, Urine Cl −^- 88 mEq/L, BP 115/75115/75 mmHgSurreptitious vomiting
  • Patient D: pH 7.507.50, PaCO 2_2 4646 mmHg, Na +^+ 139139 mEq/L, K +^+ 2.52.5 mEq/L, Cl −^- 9292 mEq/L, HCO 3−_3^- 3535 mEq/L, Urine Cl −^- 6868 mEq/L, BP 110/70110/70 mmHgSurreptitious loop diuretic abuse
  • Patient E: pH 7.517.51, PaCO 2_2 4747 mmHg, Na +^+ 142142 mEq/L, K +^+ 2.72.7 mEq/L, Cl −^- 9494 mEq/L, HCO 3−_3^- 3636 mEq/L, Urine Cl −^- 5555 mEq/L, BP 175/105175/105 mmHgPrimary hyperaldosteronism

Answer

Patient A matches with Distal (Type 1) RTA, Patient B with Hyporeninemic hypoaldosteronism, Patient C with Surreptitious vomiting, Patient D with Surreptitious loop diuretic abuse, and Patient E with Primary hyperaldosteronism.
Each patient requires a systemic approach to acid-base interpretation. Matching correctly relies on integrating multiple parameters: differentiating RTA types by potassium and urine pH, and evaluating metabolic alkalosis using urine chloride and blood pressure.

Step-by-Step Solution

1
Calculate the serum anion gap for acidotic patients
Patients A and B have a normal serum anion gap (1212 mEq/L), confirming hyperchloremic metabolic acidosis.
To classify the metabolic acidosis and determine if it is due to unmeasured anions or bicarbonate loss.
2
Evaluate potassium, urine anion gap, and urine pH in normal anion gap acidosis
Patient A has hypokalemia and urine pH >5.5> 5.5, indicating Type 11 RTA. Patient B has hyperkalemia and urine pH <5.5< 5.5, indicating Type 44 RTA.
To differentiate between renal tubular acidosis subtypes.
3
Analyze urine chloride in patients with metabolic alkalosis
Patient C has low urine Cl −^- (<20< 20 mEq/L), indicating saline-responsive alkalosis. Patients D and E have high urine Cl −^- (>20> 20 mEq/L), indicating saline-resistant alkalosis.
To determine volume status and chloride responsiveness.
4
Assess blood pressure in saline-resistant metabolic alkalosis
Patient D is normotensive, pointing to diuretic abuse. Patient E is hypertensive, pointing to primary hyperaldosteronism.
To distinguish between mineralocorticoid excess and renal salt-wasting states.

Key Concept

Interpretation of complex acid-base disorders requires algorithmic evaluation of the serum anion gap, potassium, urine pH, urine anion gap, urine chloride, and blood pressure to isolate the precise pathophysiological mechanism.
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Interpreting Laboratory Results

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