skip to main content

Type 4 RTA Drug-Induced — ESENeph MCQ

Instant feedback + full explanation. One question, done properly.

ModerateAcid-BaseType 4 RTA Drug-InducedESENeph

A 42-year-old woman presents with a non-anion gap metabolic acidosis. Serum potassium is 5.8 mmol/L. eGFR is 45 mL/min/1.73m2. She is on trimethoprim for a UTI and spironolactone for heart failure. Urine pH is 5.2. Urine anion gap is positive (+25 mEq/L). What is the most likely type of renal tubular acidosis?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: D — Type 4 RTA (hypoaldosteronism)

The combination of non-anion gap metabolic acidosis with HYPERkalaemia, positive urine anion gap, and acidic urine pH (<5.5) is characteristic of type 4 RTA. The positive urine anion gap indicates impaired renal ammonium excretion. Type 4 RTA results from aldosterone deficiency or resistance. In this patient, spironolactone blocks the mineralocorticoid receptor (aldosterone resistance), and trimethoprim blocks ENaC (mimicking amiloride). Both contribute to hyperkalaemic RTA. Type 1 RTA has HYPOkalaemia and urine pH >5.5. Type 2 RTA has hypokalaemia. GI bicarbonate loss causes a negative urine anion gap.

Reference: Rodríguez Soriano 2002 – RTA Classification; Palmer & Alpern 2011 – RTA Mechanisms