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A 16-year-old female star gymnast presents to your office complaining of fatigue, diffuse
weakness, and muscle cramps. She has no previous medical history and denies tobacco,
alcohol, or illicit drug use. There is no significant family history. Examination shows a thin
female with normal blood pressure. Body mass index (BMI) is 18 kg/m2. Oral examination
shows poor dentition. Muscle tone is normal, and neurologic examination is normal. Laboratory
studies show hematocrit of 38.5%, creatinine of 0.6 mg/dL, serum bicarbonate of 30 meq/L,
and potassium of 2.7 meq/L. Further evaluation should include which of the following?
A. Urinalysis and urine culture
B. Plasma renin and aldosterone levels
C. Urine toxicology screen for opiates
D. Urine toxicology screen for diuretics
E. Serum magnesium level

D...

D..

The answer is D.

In any patient with hypokalemia the use of diuretics must be excluded. This patient has
multiple warning signs for the use of agents to alter her weight, including her age, gender, and
participation in competitive sports. Her BMI is low, and the oral examination may suggest
chronic vomiting. Chronic vomiting may be associated with a low urine chloride level. Once
diuretic use and vomiting are excluded, the differential diagnosis of hypokalemia and metabolic
alkalosis includes magnesium deficiency, Liddle's syndrome, Bartter's syndrome, and
Gittleman's syndrome. Liddle's syndrome is associated with hypertension and undetectable
aldosterone and renin levels. It is a rare autosomal dominant disorder. Classic Bartter's
syndrome has a presentation similar to that of this patient. It may also include polyuria and
nocturia because of hypokalemia-induced diabetes insipidus. Gittleman's syndrome can be
distinguished from Bartter's syndrome by hypomagnesemia and hypocalciuria.

yes on D