Electrolyte Disorders USMLE Step 1 Practice Question
A 41-year-old woman with chronic alcoholism presents with acute pancreatitis and is hospitalized on day 2. She develops tremor, carpal spasm, and tetany. Vital signs show HR 98/min, BP 128/82 mmHg, RR 16/min, temperature 37.8°C. Laboratory studies reveal serum potassium 2.8 mEq/L (normal 3.5-5.0), magnesium 0.7 mEq/L, and calcium 8.2 mg/dL. Despite receiving 60 mEq potassium intravenously over 24 hours, her serum potassium remains 2.6 mEq/L. Urinalysis shows no glycosuria. Which mechanism best explains her refractory hypokalemia?
Answer choices
- AHyponatremia blocks potassium absorption from the gastrointestinal tract
- BHypomagnesemia increases renal potassium wastingCorrect answer
- CRespiratory acidosis prevents potassium replacement from entering cells
- DHypercalcemia increases potassium secretion in the proximal tubule
- EHypomagnesemia causes intracellular potassium shift only
- FHypophosphatemia impairs ATP production, reducing Na-K-ATPase activity in the collecting duct
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