Cystine stones are hexagonal and yield a positive nitroprusside test. Which option accurately lists cystine stones?

Cystine stones are hexagonal and yield a positive nitroprusside test. Which option accurately lists cystine stones?

• A. Calcium oxalate
• B. Struvite
• C. Cystine
• D. Uric acid

Answer: (C)

Cystine stones are identified by two characteristic features: hexagonal crystals and a positive nitroprusside test. The hexagonal shape reflects the crystal form of cystine, and the nitroprusside test detects sulfhydryl groups found in cystine, turning red when present. This combination points directly to cystine stones, which arise from cystinuria due to defective renal reabsorption of dibasic amino acids, including cystine. Other common stone types have different shapes and tests: calcium oxalate stones are often envelope- or dumbbell-shaped and typically do not give a positive nitroprusside test; struvite stones have a coffin-lid appearance and form with urease-producing infections; uric acid stones are usually rhomboid or rosette-shaped and form in acidic urine, also lacking a positive nitroprusside test. The description aligns with cystine stones, making that listing the correct match.

Cystine stones are identified by two characteristic features: hexagonal crystals and a positive nitroprusside test. The hexagonal shape reflects the crystal form of cystine, and the nitroprusside test detects sulfhydryl groups found in cystine, turning red when present. This combination points directly to cystine stones, which arise from cystinuria due to defective renal reabsorption of dibasic amino acids, including cystine. Other common stone types have different shapes and tests: calcium oxalate stones are often envelope- or dumbbell-shaped and typically do not give a positive nitroprusside test; struvite stones have a coffin-lid appearance and form with urease-producing infections; uric acid stones are usually rhomboid or rosette-shaped and form in acidic urine, also lacking a positive nitroprusside test. The description aligns with cystine stones, making that listing the correct match.