Correct.  Cystinuria is the inability to absorb the amino acid cysteine from the intestines and renal tubules.  Therefore, any cystine that may be present in ones diet (foods high in animal protein) will be excreted in the urine.  Cystine is insoluble in an acidic pH and thus will lead to the formation of renal calculi in the urinary tract or bladder if the pH environment is acidic.  Because cysteine is not an essential amino acid and can be made from methionine, there are no physiological consequences resulting from cystinuria.  However, a patient with cystinuria will be susceptible to the pain associated with renal calculi.  One option for treatment may be to increase the urine volume by drinking a lot of fluids.  This may prevent stone formation.  Another option is to choose a diet that is free of cystine.  A diet high in animal protein, similar to the one this patient was on, contains large quantities of cystine.  Vegetable proteins such as nuts and beans are low in cystine and should be considered.  An additional way of preventing the formation of renal calculi would be to alkalise the urine.  In an alkaline urine, cystine crystals dissolve so renal calculi will not form.  Medications may also be available.

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