Chronic Kidney Disease USMLE Step 1 Practice Question
A 34-year-old woman with Sjogren syndrome presents with fatigue and recurrent nephrolithiasis. Vital signs: BP 132/88 mmHg, HR 92 bpm, RR 16/min, Temp 37.2°C, SpO2 98% on room air. Laboratory studies reveal normal anion gap metabolic acidosis (pH 7.32, HCO3 18 mEq/L), serum potassium 3.1 mEq/L, and urine pH 6.3. Serum creatinine is normal. No proteinuria noted. Which of the following is the most likely underlying renal tubular defect?
Answer choices
- AImpaired hydrogen ion secretion by alpha intercalated cellsCorrect answer
- BExcess loop diuretic effect in the thick ascending limb
- CDefective bicarbonate reabsorption in the proximal tubule
- DDeficient aldosterone production causing impaired sodium reabsorption
- EConstitutive epithelial sodium channel activation in the collecting tubule
- FImpaired ammonia excretion due to defective glutaminase activity in proximal tubule cells
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