pediatrics
Cystinuria
Key Points
Defective urinary resorption of cystine increases urinary cystine levels, leading to cystine kidney stones and sometimes chronic kidney disease. Yellow-brown hexagonal crystals in the urine are pathognomonic; quantitative cystine excretion is typically>400 mg/day. Treat with increased fluid intake to give urine output of 1.5 to 2 L/m2/day, and alkalinize urine withpotassium citrateorpotassium bicarbonate. Restrict dietary sodium and animal protein. Drugs such aspenicillamine,tiopronin, orcaptoprilmay be necessary, but adverse effects are a concern. 