Abstract

BUITRAGO, Luz Mery et al. Quantitation of urinary cystine for the detection of cystinuria. Acta bioquím. clín. latinoam. [online]. 2014, vol.48, n.1. ISSN 0325-2957.

Cystinuria is an inborn error of metabolism, caused by a defect in renal tubular transport of the following aminoacids: arginine, ornithine, lysine and cystine. Accumulation of the latter poorly soluble aminoacid leads to the development of kidney stones, characteristic of the disease. In this study, an easy and dependable spectrophotometric method for the quantitative determination of urinary cystine was standardized. The analysis was performed on 184 samples from 104 controls and 80 patients with kidney stones. In order to validate the method and later establish a range of normal urinary cystine excretion in the Colombian population, the following parameters were evaluated: Accuracy, precision, linearity and lower limit of detection. The technique showed intra and intei assay coefficients of variation below 10%, and excellent linearity, with an R square (r²) coefficient between known cystine concentrations and absorbance generated by the method at 0.998. Using this technique, a normal urinary cystine excretion range of 1.35-110.11 mg cystine/g creatinine was found. Among the 80 patients with kidney stones, elevated urinary cystine levels were found in 5 of them, compatible with the presence of cystinuria. This method can be implemented in any clinical laboratory to confirm the diagnosis of cystinuria and provide opportune treatment.

Keywords : cystine; aminoaciduria; cystinuria; kidney stones; metabolism; chromatography; validation; reference values.

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