Nterassay variability of anti-HLA antibody measurement using luminex single antigen beads (SAB)

Abstract

Measurement of anti-HLA antibodies using Luminex SAB has been widely adopted, however there is no consensus about cut-off for clinically relevant cut-offs. There is little published data about the performance characteristics of these assays. Objectives: To define the interassay variability of antibody levels in patient serum. Methods: Retrospective review of internal quality control data from SAB assays performed in our laboratory over a one year period. A serum-pool prepared from multiple samples from a single, highly-sensitised patient served as an internal quality control (IQC), and was included in all runs of One Lambda SAB. The Tepnel positive control was similarly evaluated. Levy-Jennings plots were maintained for 3 beads giving high, low and borderline values. 128 runs were analysed for the one lambda SAB, while 23 runs of Tepnel SAB were included. Results: The strongly positive IQC value gave a mean MFI of 19,185 (range 13,587 to 23,023, CV 8.5%). The low-positive bead gave a mean MFI of 1154 (range 714-2090, CV 16.9%). The borderline value gave a mean MFI of 647 (range 401-1235, CV 20%). Levy-Jennings plots showed significantly decreased lab temperature on MFIs for all beads rose significantly when the laboratory temperature dropped. Interassay CV was lower for the Tepnel assay with weak values, but greater with strongly positive values. The strongly positive bead showed a mean adjusted-value 3 of 47 (range 32-113, CV 28.4%). The medium bead showed a mean adjusted-value 3 of 10.9 (range 8.6-14.6, CV 13.1%), while the low IQC showed an adjusted-value 3 of 6.49 (range 5.4 -7.5, CV 9.4%). Conclusion: Luminex SAB assays show significant interassay variability, within a single laboratory. Manufacturers should improve the quality of asays. Despite apparent simplicity, SAB assays should be interpreted by experienced H & I personnel.