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Proximal RTA – Fanconi syndrome — RACP Paediatrics MCQ

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HardNephrologyProximal RTA – Fanconi syndromeRACP Paediatrics

A 3-year-old with Fanconi syndrome (glycosuria, aminoaciduria, phosphaturia, bicarbonaturia) has a normal anion gap metabolic acidosis. Urine pH is variable but can acidify below 5.5 when serum bicarbonate is very low. There is associated rickets. What is the most likely type of RTA?

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Correct answer: B — Type 2 (proximal) RTA

Proximal (type 2) RTA involves impaired bicarbonate reabsorption in the proximal tubule. It often occurs as part of generalised proximal tubular dysfunction (Fanconi syndrome) with glycosuria, aminoaciduria, and phosphaturia. Unlike distal RTA, the urine CAN be acidified to <5.5 when serum bicarbonate falls below the reabsorptive threshold. Higher bicarbonate doses are needed.

Reference: RCH Melbourne – 2023 – RTA CPG; RACP Paediatric Curriculum – Nephrology