A 60-year-old woman with long-standing type 2 diabetes has eGFR 38 mL/min, potassium 5.9 mEq/L, bicarbonate 19 mEq/L, chloride 111 mEq/L, anion gap 12 mEq/L, and glucose 150 mg/dL. Arterial pH is 7.33. Plasma aldosterone and plasma renin activity are both low. What is the most likely diagnosis?
- A Type 1 distal renal tubular acidosis
- B Type 2 proximal renal tubular acidosis
- C Type 4 renal tubular acidosis due to hyporeninaemic hypoaldosteronism ✓
- D Early diabetic ketoacidosis
Correct answer: C. Type 4 renal tubular acidosis due to hyporeninaemic hypoaldosteronism
Explanation
Diabetic CKD commonly produces hyporeninaemic hypoaldosteronism, giving type 4 RTA: hyperkalaemic, hyperchloraemic normal anion gap acidosis with low renin and low aldosterone. The hyperkalaemia distinguishes it decisively from type 1 and type 2 RTA, both of which cause hypokalaemia. Glucose is near normal and the anion gap is normal, excluding ketoacidosis, which would produce a high anion gap acidosis.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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