What is the significance of the sodium nitroprusside test?

To test Cystinuria. Cystinuria is an autosomal recessive disease, which means one needs two copies of the defective gene (one inherited from each parent who are asympto) are needed to be born w the disease. It causes cysteine crystals to form & kidney stones & causes kidney disease & Pain. Adding Nitroprusside to a baby's urine turns dark if cysteine is present in high concentration. If + cystinuria can be treated.