Twenty-four-hour urine oxalate and risk of chronic kidney disease.

Background: To assess whether 24-h urine oxalate (UOx) excretion is a risk factor for incident chronic kidney disease (CKD).

Methods: This longitudinal observational USA-based study included 426 896 individuals aged ≥18 years with no CKD at baseline and with at least one UOx, and at least 6 months of baseline and 6 months of follow-up data. Of these, 11 239 (2.6%) had an underlying malabsorptive condition. Incident CKD, defined by relevant International Classification of Diseases codes, was identified from a multi-source data cloud containing individual-level healthcare claims and electronic medical records data. The association between categories of UOx and incident CKD was modeled using logistic regression adjusting for age, sex, race, body mass index, baseline urine calcium, urine citrate, urine volume, tobacco use, hypertension, diabetes, malabsorption and cardiovascular disease.

Results: Mean follow-up time was 38.9 months (standard deviation 21.7). Compared with individuals with UOx <20 mg/24 h, the odds of developing incident CKD increased for UOx 20-29 mg/24 h [multivariable-adjusted odds ratio (MVOR) 1.14 (95% CI 1.07, 1.21)] through 80+ mg/24 h [MVOR 1.35 (1.21, 1.50)] and was statistically significant for each UOx category. A similar pattern was seen in the subgroup with a malabsorptive condition though the magnitudes of association were larger, with the odds of developing incident CKD increased for UOx 20-29 mg/24 h [MVOR 1.50 (1.03, 2.20)] through 80+ mg/24 h [MVOR 2.34 (1.50, 3.63)] as compared with UOx <20 mg/24 h.

Conclusions: The risk of incident CKD increases with increasing 24-h UOx excretion. Future studies should examine whether reducing UOx diminishes the risk of developing CKD.