Acute Kidney Injury USMLE Step 1 Practice Question
A 54-year-old man presents for follow-up 3 weeks after emergency percutaneous coronary intervention for ST-elevation myocardial infarction. During hospitalization, he developed acute kidney injury requiring close monitoring. His serum creatinine peaked at 3.2 mg/dL on hospital day 3 but has since declined. He now reports polyuria with urine output exceeding 4 L/day. Current laboratory values show serum creatinine 1.6 mg/dL, BUN 20 mg/dL, serum potassium 2.8 mEq/L (normal 3.5-5.0), serum sodium 128 mEq/L (normal 135-145), serum magnesium 1.4 mg/dL (normal 1.7-2.2), and serum phosphate 2.1 mg/dL (normal 2.5-4.5). Which of the following best explains the current electrolyte abnormalities and represents the primary concern requiring intervention?
Answer choices
- AHyperkalemia due to continued renal tubular dysfunction and reduced urinary potassium excretion
- BMetabolic alkalosis from loss of hydrogen ions in dilute urine during the polyuric phase
- CHypokalemia from enhanced urinary potassium wasting during tubular recovery with intact glomerular filtrationCorrect answer
- DHypermagnesemia secondary to decreased glomerular filtration rate and impaired tubular magnesium reabsorption
- EHypernatremia from prerenal azotemia and increased insensible fluid losses
- FHyperphosphatemia from impaired phosphate filtration and secondary hyperparathyroidism
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