Which urine crystal is most likely seen in acidic urine?

• A. Calcium phosphate
• B. Uric acid
• C. Ammonium magnesium phosphate
• D. Cystine

Answer: (B)

The main idea here is that urine pH influences which crystals are most likely to form. Uric acid crystals favor acidic conditions because low pH reduces uric acid’s solubility, so it precipitates more readily as crystals. The pH also shifts uric acid toward its nonionic form, which is less soluble in urine, promoting crystallization. That’s why in an acidic urine sample you’d most often expect to see uric acid crystals, which on microscopy can appear as yellow to amber rhomboid or rosette-shaped crystals.

Calcium phosphate tends to precipitate in alkaline urine, not acidic, so it’s less likely in acidic samples. Ammonium magnesium phosphate (struvite) also favors alkaline urine and is commonly linked to infection with urease-producing bacteria. Cystine crystals can appear with certain metabolic disorders like cystinuria and are hexagonal in shape; while they can occur in acidic urine, they are not the classic or most common finding for acidity, making uric acid the best answer in this context.