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Distal RTA — RACP Adult Medicine MCQ

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ModerateNephrologyDistal RTARACP Adult Medicine

A 50-year-old man with known type 1 renal tubular acidosis (distal RTA) presents with muscle weakness. ABG shows pH 7.28, HCO₃⁻ 14 mmol/L. Na⁺ 140, K⁺ 2.8, Cl⁻ 116 mmol/L. Urine pH is 6.5 despite systemic acidosis. What is the most likely renal tubular disorder?

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Correct answer: B — Type 1 (distal) RTA

Non-anion gap metabolic acidosis (AG = 140-116-14 = 10, normal) with hypokalaemia and inappropriately alkaline urine (pH >5.5) despite systemic acidosis is diagnostic of type 1 (distal) RTA. The distal tubule cannot secrete H⁺ to acidify urine. It is associated with nephrocalcinosis and kidney stones. Treatment is oral sodium bicarbonate or potassium citrate.

Reference: eTG Nephrology – 2024 – Renal Tubular Acidosis; KDIGO 2024