UTI and renal failure due to obstruction may develop. Radiopaque cystine stones form in the renal pelvis or bladder. Staghorn calculi are common. Cystine may occur in the urine as yellow-brown hexagonal crystals. Excessive cystine in the urine may be detected by the nitroprusside cyanide test.
Diagnosis is confirmed by chromatography or electrophoresis.
In longtime survivors, end-stage renal disease is the rule. The urinary concentration of cystine can be reduced by increasing urine volume. Hydration is important at night when urinary pH drops. When high fluid intake and alkalinization do not reduce stone formation, other medications may be tried, eg, penicillamine, although toxicity limits its usefulness. About half of all patients treated with penicillamine develop some toxic manifestation, including fever, rash, arthralgias, and, less commonly, nephrotic syndrome, pancytopenia, or SLE-like reaction.