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Type 4 RTA — ESENeph MCQ

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HardAcid-BaseType 4 RTAESENeph

A patient with type 4 (hyperkalaemic) renal tubular acidosis has CKD G3b secondary to diabetic nephropathy. She has a potassium of 6.0 mmol/L and bicarbonate of 18 mmol/L. Her renin and aldosterone are both low. She is on Ramipril. What is the underlying mechanism?

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Correct answer: D — Hypoaldosteronism (hyporeninemic hypoaldosteronism) exacerbated by RASi

Type 4 RTA is characterised by hyperkalaemia and mild metabolic acidosis due to aldosterone deficiency or resistance. In diabetic nephropathy, it is most commonly caused by hyporeninemic hypoaldosteronism (low renin → low aldosterone). RAS inhibitors exacerbate this by further suppressing aldosterone. The combination of diabetic nephropathy, low renin, low aldosterone, and ACEi use is the classic clinical scenario. Management includes dietary potassium restriction, fludrocortisone (rarely used), or potassium binders.

Reference: Rodríguez-Soriano 2002 – RTA Review; KDIGO 2024 – CKD