Analytical and clinical validation of a competitive ELISA for serum indoxyl sulfate and its clinical association with chronic kidney disease risk stratification

BACKGROUND: Indoxyl sulfate (IS), a protein-bound uremic toxin derived from tryptophan metabolism, accumulates in patients with chronic kidney disease (CKD) and contributes to renal, vascular, and systemic injury. Conventional detection using LC-MS/MS is accurate but resource-intensive. To simplify IS quantification, Leadgene Biomedical developed a competitive enzyme-linked immunosorbent assay (ELISA) that employs anti-IS monoclonal antibodies capable of recognizing both free and protein-bound IS forms. METHODS: IS ELISA Kit. Diagnostic performance was assessed through ROC analysis, precision by nested-ANOVA (total %CV < 10%), and accuracy by comparison with LC-MS/MS. The ELISA demonstrated excellent diagnostic performance with an area under the curve of 0.96 and an optimal cutoff of 2.233 µg/mL, yielding sensitivity 0.872 (95% confidence interval (CI) 0.816-0.912) and specificity 0.940 (95% CI 0.856-0.977). The Pearson correlation coefficient between the ELISA and LC-MS/MS results was 0.964, confirming high analytical concordance. CONCLUSION: IS ELISA Kit provides a rapid and accessible platform for serum indoxyl sulfate quantification with validated analytical performance and significant association with higher-risk CKD classification.