A 62-year-old woman with type 2 diabetes, hypertension, and CKD stage 3a (eGFR 48 mL/min) has serum K+ 6.4 mEq/L on lisinopril and spironolactone. BP is well controlled. She has no ECG changes. After stopping spironolactone, K+ remains 5.9 mEq/L. Plasma renin is low and plasma aldosterone is low. Which is the MOST likely underlying mechanism?

• A Type 1 distal renal tubular acidosis
• B Hyporeninemic hypoaldosteronism (type 4 RTA) ✓
• C Primary adrenal insufficiency (Addison disease)
• D Gordon syndrome (pseudohypoaldosteronism type II)

Explanation

Hyporeninemic hypoaldosteronism (type 4 RTA) is common in diabetic CKD and causes hyperkalaemia with normal anion gap metabolic acidosis due to low renin and low aldosterone. Distractor C (Addison) gives elevated ACTH and hyperpigmentation with high renin and low aldosterone, not low renin. Distractor A (type 1 RTA) gives hypokalemia, not hyperkalemia. Distractor D (Gordon) causes hypertension and hyperkalemia but with suppressed aldosterone in the setting of WNK kinase mutation.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.