Cystine as a risk factor of the stone formation in kidney: the reference value range of urinary excretion, the stage diagnosis of cystine metabolism disorder

Objective: to define the reference value ranges of cystine, lysine and arginine urinary excretion relative to creatinine in the morning urine samples for the metabolic disorders diagnosis leading to the formation of urinary stones. Materials and methods: the study involved 695 healthy individuals aged 1-17 and 1564 patients with urolithiasis aged 7-45. The content of cystine in the urine samples was determined by high performance liquid chromatography. The chemical composition of urinary stones was investigated by methods of the qualitative chemical reaction and the crystals microscopy. Results: the reference value ranges of cystine, lysine and arginine urinary excretion relative to creatinine in the morning urine samples were developed in the age aspect. Excess in cystine level in the urine samples of the relatively healthy individuals detected in 1.4% of cases. From 1564 urinary stones submitted for analysis, the frequency of cystine stones was 0.8%. Conclusion: for the objective assessment of the cystine metabolism status the evaluation of the degree of cystinuria is necessary in order to form the risk group for cystine nephrolithiasis. The reference value ranges of cystine urinary excretion developed in the age aspect and «cystine / creatinine index» in morning urine samples will provide the opportunity to identify the state of the cystine exchange from early childhood and develop differentiated program for the prevention of stone formation in the kidneys.

cysteine, lysine, arginine, urine, the reference value range, urolithiasis