Cystinuria — ESENeph MCQ
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Correct answer: E — Quantify cystine in a 24-hour urine collection
The best answer is “Quantify cystine in a 24-hour urine collection”. Hexagonal crystals are characteristic of cystine, and quantitative urinary cystine can confirm cystinuria when a stone is unavailable for analysis. The strong familial early-onset pattern supports the inherited amino-acid transport defect. “Serum urate concentration” is less appropriate because urate does not confirm a cystine transport disorder “Plasma metanephrines” is less appropriate because these investigate catecholamine-secreting tumours rather than stone composition “Anti-GBM antibody testing” is less appropriate because anti-GBM disease causes rapidly progressive nephritis, not hexagonal crystals “Faecal calprotectin” is less appropriate because intestinal inflammation testing does not establish cystinuria
Reference: EAU urolithiasis metabolic evaluation guideline: https://uroweb.org/guidelines/urolithiasis/chapter/metabolic-evaluation-and-recurrence-prevention