A 55-year-old woman on long-term tenofovir disoproxil fumarate for HIV develops proximal tubular dysfunction with glucosuria (euglycemic), phosphaturia, aminoaciduria, and low serum uric acid. Serum bicarbonate is 16 mEq/L, urine pH is 5.5. This is consistent with:
- A Distal (Type 1) renal tubular acidosis
- B Type 4 RTA (hyperkalemic)
- C Fanconi syndrome with proximal (Type 2) RTA ✓
- D Diabetic nephropathy
Correct answer: C. Fanconi syndrome with proximal (Type 2) RTA
Explanation
Fanconi syndrome (generalised proximal tubular dysfunction) manifests as phosphaturia, glycosuria, aminoaciduria, and uricosuria, combined with proximal (Type 2) RTA showing low serum bicarbonate and urine pH that can acidify normally when bicarbonate is below the proximal reabsorption threshold. TDF causes mitochondrial toxicity in proximal tubule cells. Type 1 RTA cannot acidify urine below 5.5 even with acidemia. Type 4 RTA shows hyperkalemia and is associated with hypoaldosteronism.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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