Acid-Base Disorders USMLE Step 1 Practice Question
A 19-year-old man presents with growth delay, proximal muscle weakness, and polyuria. Vital signs show BP 105/68 mmHg, HR 88/min, RR 16/min, temp 37°C, SpO2 98% on room air. Laboratory studies reveal normal anion gap metabolic acidosis (pH 7.32, HCO3− 16 mEq/L), serum potassium 2.8 mEq/L, serum glucose 95 mg/dL with glucosuria, aminoaciduria, and phosphaturia. Urine pH is appropriately acidic. Which renal tubular defect most likely explains this clinical presentation?
Answer choices
- AImpaired H+ secretion by alpha intercalated cells
- BExcessive ammonium production by the kidney
- CDecreased aldosterone synthesis in the adrenal cortex
- DIncreased sodium chloride reabsorption in the distal convoluted tubule
- EImpaired bicarbonate reabsorption in the proximal tubuleCorrect answer
- FImpaired organic anion secretion in the proximal tubule
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