skip to main content

Citrate Inhibitor Mechanism Calcium Stones — ESENeph MCQ

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

ModerateRenal Stone DiseaseCitrate Inhibitor Mechanism Calcium StonesESENeph

A 39-year-old man with CKD G3a (eGFR 50 mL/min/1.73m2) has recurrent calcium oxalate stones. His 24-hour urine citrate excretion is low at 0.8 mmol/day (normal >1.7 mmol/day). Urine pH is 5.5. He has no metabolic acidosis. What is the mechanism by which citrate prevents calcium stone formation?

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

Reveal the answer and explanation

Correct answer: D — Citrate inhibits calcium oxalate and calcium phosphate crystal nucleation and growth by chelating urinary calcium

Citrate is the most important endogenous inhibitor of calcium stone formation. It chelates ionic calcium in the urine, reducing the saturation of calcium oxalate and calcium phosphate, thereby inhibiting crystal nucleation, growth, and aggregation. Hypocitraturia is a major risk factor for calcium stones and is common in CKD (due to metabolic acidosis, which increases proximal tubular citrate reabsorption). Potassium citrate supplementation is the treatment — it provides citrate directly and also alkalinises urine (beneficial for uric acid stones). Sodium citrate is an alternative but sodium loading increases calcium excretion, partially negating the benefit.

Reference: https://guidelines.ukkidney.org