ELECTROLYTE QUIZ

The answer to the electrolyte quiz of June 17, 2012 is  C.

An 18-year-old female with anorexia nervosa is found on routine laboratory examination to be hypokalemic.

Laboratory Studies

Serum sodium 134 mEq/L

Serum potassium 3.1 mEq/L

Serum chloride 92 mEq/L

Serum bicarbonate 31 mEq/L

Blood urea nitrogen 5 mg/dL

Serum creatinine 0.7 mg/dL

Urine chloride 42 mEq/L

24 hour urine calcium 310 mg

Which of the following is the most likely cause of this patient’s laboratory findings:

A. Laxative abuse

B. Gitelman syndrome

C. Loop diuretic abuse

D. Surreptitious vomiting

E. Thiazide diuretic abuse

Explanation

This patient also has hypokalemic metabolic alkalosis with high urine chloride. The additional finding of hypercalciuria (>250 mg/d in females) narrows the differential diagnosis down to Bartter (usually presents in infancy or early childhood) and loop diuretic abuse (common in anorexics).


(Source: Dr. Alan Yu, Professor of Medicine, The Kidney Institute, UKMC, Kansas)