Urine Anion Gap Interpretation — ESENeph MCQ

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

HardAcid-BaseUrine Anion Gap InterpretationESENeph

A patient has bicarbonate 15 mmol/L, chloride 116 mmol/L, potassium 2.9 mmol/L, urine pH 5.0 and a negative urine anion gap after several days of watery stool. What is the most likely cause?

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

Reveal the answer and explanation

Correct answer: C — Gastrointestinal bicarbonate loss from diarrhoea

The best answer is “Gastrointestinal bicarbonate loss from diarrhoea”. A negative urine anion gap indicates increased ammonium chloride excretion, showing that the kidneys are responding appropriately. Combined with diarrhoea and hypokalaemic normal-gap acidosis, this localises bicarbonate loss to the gut. “Distal renal tubular acidosis” is less appropriate because distal RTA usually has inappropriately high urine pH and impaired ammonium excretion “Vomiting-induced metabolic alkalosis” is less appropriate because vomiting raises bicarbonate rather than producing this hyperchloraemic acidosis “Diabetic ketoacidosis” is less appropriate because ketoacidosis produces a high anion gap rather than this pattern “Primary respiratory alkalosis” is less appropriate because the biochemical pattern is a metabolic bicarbonate deficit

Reference: KDIGO 2024 CKD guideline: https://kdigo.org/wp-content/uploads/2024/03/KDIGO-2024-CKD-Guideline.pdf