Luminex MFI-Efforts from a Qualitative to a Quantitative Analysis

The Luminex multiplex assay for the definition of HLA antibodies was introduced 20 years ago. To date, although the assay is simple and straightforward, the interpretation of the results remains a conundrum. Making use of the so-called mean fluorescence value only does not help since this value is relative, the day-to-day variation is significantly large, and the user variation is beyond acceptable ranges. Within the same range of problems, the cutoff value used to classify HLA-specific antibodies as being either present or absent varies between laboratories. This threshold influences clinical decision-making. In addition, the readout value is used to diagnose the amount of HLA-specific antibodies after treatments like absorption, plasmapheresis, or transplantation, overlooking the relative nature of the value. In this study, we show bead variability for HLA class I and HLA class II based on negatively defined bead reactions with a mean fluorescence value below 1500 and self-antigens. In an effort to circumvent the assay's inherent problems, we introduced the term ratio. For each serum sample, a paired sample from before the treatment is run in parallel. The ratio of post-treatment to pre-treatment can then be used to characterize antibody dynamics: a ratio above 1 reflects increased antibody production and a ratio below 1 indicates a decrease in antibodies in the serum. This value may offer the possibility to make more informed and adaptive treatment decisions.