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Difficulty: MediumNephrology

Correlate the following clinical conditions with their most characteristic acid-base and electrolyte laboratory profile.

  • Surreptitious vomitingHypokalemic metabolic alkalosis, urine chloride <20< 20 mEq/L, normotension or hypotension
  • Primary hyperaldosteronismHypokalemic metabolic alkalosis, urine chloride >20> 20 mEq/L, hypertension
  • Thiazide diuretic abuseHypokalemic metabolic alkalosis, urine chloride >20> 20 mEq/L, normotension or hypotension
  • Severe acute diarrheaNormal anion gap metabolic acidosis, hypokalemia

Answer

Surreptitious vomiting is matched with low urine chloride metabolic alkalosis; Primary hyperaldosteronism with high urine chloride metabolic alkalosis and hypertension; Thiazide abuse with high urine chloride metabolic alkalosis and normotension; Severe acute diarrhea with normal anion gap metabolic acidosis.
Surreptitious vomiting causes saline-responsive alkalosis (low urine chloride). Thiazide abuse causes saline-resistant alkalosis (high urine chloride) with volume depletion. Primary hyperaldosteronism causes saline-resistant alkalosis (high urine chloride) with volume expansion (hypertension). Diarrhea causes a non-anion gap metabolic acidosis due to direct gastrointestinal base loss.

Step-by-Step Solution

1
Differentiate the causes of hypokalemic metabolic alkalosis based on blood pressure.
Hypertension points to mineralocorticoid excess (Primary hyperaldosteronism). Normotension or hypotension points to volume contraction (vomiting or diuretic use).
Volume status helps narrow down the etiology of metabolic alkalosis.
2
Differentiate the volume-contracted causes of metabolic alkalosis using urine chloride.
Urine chloride <20< 20 mEq/L indicates an extrarenal cause of chloride loss where the kidneys are functioning properly to retain chloride (surreptitious vomiting). Urine chloride >20> 20 mEq/L indicates renal chloride wasting (thiazide diuretic abuse).
Urine chloride distinguishes saline-responsive (extrarenal) from saline-resistant (renal) chloride losses.
3
Identify the primary acid-base disorder caused by severe lower gastrointestinal fluid loss.
Loss of bicarbonate-rich fluid results in a normal anion gap metabolic acidosis.
Unlike gastric fluid which is acidic, lower gastrointestinal fluid is rich in bicarbonate and potassium.

Key Concept

Differentiation of acid-base disorders using volume status, blood pressure, and urine chloride.
Estimated Time:1m 30s
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Topics

Nephrology

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