Higher urinary oxalate excretion is linked to an increased risk of progressive chronic kidney disease (CKD), reports a study in JAMA Internal Medicine.
The analysis included 3123 patients with stage 2 to 4 CKD, drawn from the Chronic Renal Insufficiency Study. Twenty-four-hour urinary oxalate excretion was measured at enrollment in 2003–08. Median oxalate excretion was 18.6 mg/24 hours; this value was inversely correlated with estimated glomerular filtration rate (eGFR) and positively correlated with 24-hour proteinuria.
Progression of CKD was evaluated in 2003–08, with a total follow-up of 22,318 person-years. At follow-up, 752 patients had developed end stage renal disease (ESRD), while 940 patients had reached the composite endpoint of a 50% decline in eGFR or ESRD. Both risks were significantly elevated for patients with higher oxalate excretion. From the highest to the lowest quintile (27.8 versus 11.5 mg/24 hours), hazard ratios were 1.33 for CKD progression and 1.45 for ESRD.
The association was nonlinear, with a threshold effect for patients in the third to fifth quintiles. Using the 40th percentile of oxalate excretion as a cutoff point, hazard ratios were 1.32 for CKD progression and 1.37 for ESRD.
High levels of urinary oxalate—a potentially toxic terminal metabolite—are known to be associated with acute kidney injury and CKD in certain disease states. This prospective cohort study reports that higher urinary oxalate excretion is an independent risk factor for CKD progression and ESRD. If confirmed, the findings may point to future studies evaluating the benefit of treatments to lower oxalate excretion in CKD patients [Waikar SS, et al. Association of urinary oxalate excretion with the risk of chronic kidney disease progression. JAMA Intern Med 2019; DOI: 10.1001/jamainternmed.2018.7980].