Analytical Evaluation of Urinary CXCL10 as a Biomarker for Kidney Allograft Rejection

BACKGROUND: Urinary C-X-C motif chemokine ligand 10 (CXCL10), a chemokine for leukocyte recruitment, is a sensitive and specific biomarker for diagnosing kidney transplant rejection. We performed comprehensive test validations for CXCL10 using urine samples with the Meso Quickplex SQ 120, following CLSI guidelines. METHODS: Precision, linearity, recovery, freeze-thaw cycles, interference from hemoglobin, triglyceride, conjugated bilirubin, and protein, as well as lot-to-lot variation were assessed. Fresh urine samples were held at room temperature (RT) for 1, 2, 4 h or at 4°C for 1, 2, 4, 24 h before processing, then centrifuged at different speeds (400, 800, 1500, and 2000g) and for different time periods (6, 10, and 20 min) at the same temperature. RESULTS: Within-run and between-run precision were <7% and <15% for both QC and human urine, with the latter being slightly larger. Linearity was up to 900 ng/L with a limit of quantitation of 2.45 ng/L. The recovery for urinary CXCL10 ranged from 94% to 102%. CXCL10 was stable for up to 6 freeze-thaw cycles. No interferences were detected with proteinuria and bilirubinuria. Lipuria and severe hematuria (hemoglobin, Hb = 5 g/L) were found to interfere with CXCL10 measurements. CXCL10 is stable in unprocessed urine stored at RT for 4 h and at 4°C for 24 h. Various centrifugation time and speeds had insignificant effects on CXCL10 measurement. CONCLUSIONS: Urinary CXCL10 exhibits robust reproducibility and can be handled the same way as other clinical urine analytes, indicating it is suitable as a diagnostic biomarker to assess patients after kidney transplant.