A 62-year-old man with long-standing diabetic nephropathy has Na 138, K 5.9, Cl 112, HCO3 17 mEq/L, arterial pH 7.33, creatinine 2.4 mg/dL, and urine pH 5.2. Renin and aldosterone levels are both low. The most likely diagnosis is:

• A Type 4 renal tubular acidosis ✓
• B Type 2 (proximal) renal tubular acidosis
• C Type 1 (distal) renal tubular acidosis
• D Diarrhea-induced metabolic acidosis

Explanation

Type 4 RTA is hyporeninemic hypoaldosteronism, classically seen in diabetic nephropathy, producing hyperkalemic, hyperchloremic normal anion gap acidosis. Aldosterone deficiency impairs ammoniagenesis and distal Na reabsorption. Unlike type 1 RTA, urine pH can fall below 5.5 because alpha-intercalated cell H secretion is intact. Low renin and aldosterone exclude types 1 and 2, and diarrhea would give a low serum potassium.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.