A reliable LC-MS/MS method for urinary oxalate determination and its comparison with analogous assays

The quantification of urinary oxalate is essential for the diagnosis of primary hyperoxaluria. This study sought to develop a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for urinary oxalate determination and to evaluate its concordance with an established in-house high-performance liquid chromatography (HPLC) method and a commercial LC-MS/MS assay.

The newly developed LC-MS/MS method invloved the quantification of urinary oxalate through a straightforward single-step derivatization process using o-phenylenediamine at 120 °C for 20 min. A total of 291 urine samples were analyzed using both the in-house LC-MS/MS and HPLC methods, while 94 urine samples were evaluated using both our in-house LC-MS/MS method and a commercial LC-MS/MS assay. Additionally, a reference interval for 24-hour urinary oxalate in Chinese adults was established.

Oxalate exhibited strong analytical retention in reverse-phase liquid chromatography. The newly developed LC-MS/MS method demonstrated excellent linearity with a correlation coefficient exceeding 0.995, and acheived recovery rates ranging from 92.80 % to 98.73 %. The intra-assay and inter-assay coefficients of variation (CVs) were between 0.79 % to 7.46 %, with a total CV ranging from 2.07 % to 7.50 %. No significant matrix effect was observed. However, discrepancies were identified between the in-house LC-MS/MS method and both the commercial LC-MS/MS assay and the HPLC method. The reference interval was established at 0.12-1.04 mmol/24 h (10.8-93.6 mg/24 h).

The developed LC-MS/MS method is robust and simple, providing a reliable tool for the clinical assessment of urinary oxalate. An accurate method is essential for screening analyses in primary hyperoxaluria.