Comparison of urinary citrate between patients with nephrolithiasis and healthy controls

Abstract

Objectives : Low urinary citrate excretion is a frequent metabolic abnormality found in kidney stone patients. The currently used definition of hypocitraturia (urinary citrate < 320 mg/day) may not be applicable for Thai population since a large proportion of healthy controls are classified as hypocitraturic. The present study was aimed to determine urinary citrate level in nephrolithiasis patients compared to healthy controls, to evaluate diagnostic power of urinary citrate determination as well as to establish a hypocitraturic cutoff for Thais.

Methods : One - hundred and fourteen patients with nephrolithiasis and 90 healthy subjects were recruited. Urinary citrate was measured by citrate lyase method. Receiver operating characteristic (ROC) curve analysis was performed to assess the diagnostic power of the test and fine an appropriate cutoff point. Logistic regression was carried out to quantify magnitude of association between hypocitraturia and nephrolithiasis.

Results : Nephrolithiasis patients excreted urinary citrate significantly lower than the controls. ROC analysis revealed an area under curve of 0.806 (95%CI; 0.744 - 0.864). The cutoff point at < 200 mg/day was chosen to define hypocitraturic state. Sensitivity and specificity of the test were 84.21% and 64.44%, respectively. Hypocitrauria in healthy and nephrolithiasis groups were accounted for 35.56% and 84.21%, respectively. A significant association between hypocitraturia and nephrolithiasis was observed with adjusted odds ratio of 9.62 (95%CI; 4.92 - 18.78). Patients with uric acid stone trended to excrete urinary citrate lower than those with other types, although there was no statistical significance.

Conclusion : Hypocitraturia was a significant metabolic disturbance in Thai nephrolithiasis patients. Its definition for the Thais should be re-set to < 200 mg/day in order to increase specificity and reduce false positive rate. Combination of urinary citrate with other metabolic risk factors would improve the power of diagnosis and identification of individuals at risk of kidney stone formation.