Evaluating the associations between urinary excretion of magnesium and that of other components in calcium stone-forming patients.

PURPOSE: Magnesium plays numerous vital roles in human's body. It is known as a protective factor in stone formation by binding to oxalate in the intestinal and urinary system, and decreasing its absorption and crystallization, respectively. Due to controversies about the association between the 24-h urine magnesium and other urine metabolites in different studies, this study was designed to find a clear answer to this question.

METHODS

In this retrospective cross-sectional study, data from 24-h urinalysis of the calcium stone-forming (CSF) patients were assessed. The correlation between 24-h urine (24-U) magnesium to creatinine ratio (Mg/Cr) with other 24-U metabolites to creatinine ratio was assessed, using Spearman correlation test. The association between 24-U magnesium and 24-U oxalate was also studied in a multivariate logistic regression model.

RESULTS

Among 965 patients, the level of Mg/Cr showed a direct association with all other 24-U metabolite to Cr ratio (p-value < 0.001 for all analyses). The result of multivariate regression analysis showed that the higher quartile of 24-U oxalate (> 47 mg/24 h) increased the odds of 24-U magnesium more than 75 mg/24 h (data median) (OR 1.89, 95% CI 1.14-3.13) comparing with the lower quartile of 24-U oxalate (≤ 26 mg/24 h).

CONCLUSIONS

In a routine dietary habit, since rich sources of magnesium contain a high amount of oxalate at the same time, it is not surprising that magnesium level in 24-h urinalysis showed a direct association with 24-h urine oxalate.