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

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.

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.

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.

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.