A resident is evaluating four patients who all present with significant hypokalemia and metabolic alkalosis. Pair each patient's specific clinical and laboratory profile with the most likely underlying etiology.
- A 24-year-old woman with a BMI of 18 kg/m², normal blood pressure, and a spot urine chloride concentration of 12 mEq/L.Surreptitious vomiting
- A 28-year-old healthcare worker with normal blood pressure, an extensive medication history, and a spot urine chloride concentration of 55 mEq/L.Thiazide or loop diuretic abuse
- A 42-year-old man with blood pressures consistently >160/100 mm Hg, elevated plasma aldosterone, and undetectable plasma renin activity.Primary hyperaldosteronism
- A 65-year-old man with severe hypertension, an abdominal bruit, elevated plasma aldosterone, and elevated plasma renin activity.Renovascular hypertension
Answer
The normal-blood-pressure patient with low urine chloride matches surreptitious vomiting; the normal-blood-pressure patient with high urine chloride matches diuretic abuse; the hypertensive patient with low renin matches primary hyperaldosteronism; and the hypertensive patient with high renin matches renovascular hypertension.
Evaluating hypokalemic metabolic alkalosis requires a structured approach. First, assess blood pressure. If normal, use urine chloride to distinguish GI losses (low Cl) from renal losses (high Cl). If hypertensive, use the aldosterone-to-renin ratio to differentiate primary (low renin) from secondary (high renin) hyperaldosteronism.
Step-by-Step Solution
Key Concept
Algorithm for evaluating hypokalemic metabolic alkalosis using blood pressure, urine chloride, and renin-aldosterone levels.