A simple, fast, high-throughput, modified method for the simultaneous determination of citrate and oxalate in a single purified urine sample using two commercially available kits

Background: Urine citrate and oxalate levels are risk markers for renal stone formation. Urine citrate measurements are prone to interferences and linearity issues. This study investigates modification of sample preparation for citric acid assay using the pH adjusted purified urine sample used for oxalate analysis. Methods: Urine samples were diluted 1:1 with sample diluent (Trinity Biotech Oxalate), vortexed and pH adjusted to between 6 and 8. Diluted samples were transferred into sample purifier tubes (Trinity Biotech Oxalate), vortexed, placed on a roller for 5min, spun, filtered, followed by citrate(Enzytec Liquid citrate) and oxalate(Trinity Biotech Oxalate) analysis with 12min run time per 20 samples (Indiko- Plus platform). Results: Within-run imprecision for this modified citrate method was 3.94% CV (0.47 mmol/L) and 1.02% CV (2.09 mmol/L). For oxalate this was 2.98% CV (0.28 mmol/L) and 0.86% CV (1.00 mmol/L). Linearity was confirmed up to 4 mmol/L and 3 mmol/L for oxalate and citrate respectively. Detection limits for oxalate and citrate was 0.01 mmol/L and 0.1 mmol/L respectively. Conclusions: Sample preparation for Enzytec Liquid Citric Acid was implemented using the pH adjusted, purified urine from the Trinity Biotech Oxalate kit. This method of sample preparation for the simultaneous determination of urine citrate and oxalate resulted in fast cost-effective, high throughput methods.