P039 : CORRELATION OF FLOW HLA ANTIBODY SCREENING AND LUMINEX SINGLE ANTIGEN BEAD ASSAY

Abstract

Introduction Solid phase HLA antibody detection is more sensitive and specific compared to traditional CDC tests. Different solid phase methods use different platforms. FlowPRA uses 30 beads coated with HLA antigens of 30 individuals representing the most common HLA antigens. Luminex single antigen bead assay (LSA) uses up to 100 beads, each of which is coated with antigen molecules of a single specificity, and has much better coverage of the HLA antigens. Aims This study was to determine a correlation between FlowPRA and LSA in regarding if a negative FlowPRA would correlated to a negative LSA assay. Methods We use FlowPRA for screening and LSA for identification. Every new heart and lung transplant candidate is evaluated for presence of HLA antibodies by performing both FlowPRA and LSA up front. The routine cutoff of LSA is MFI = 1000. For this study we retrospectively reviewed records of FlowPRA and LSA performed in 100 new heart transplant candidates evaluated between April – December 2013. Results Of these 100 heart transplant candidates, 37 had either class I and/or class II LSA detectable antibodies. Among these 37 patients, 32 had LSA class I antibodies, 14 had LSA class II antibodies, and 9 had both class I and II antibodies. Among these 32 patients with positive LSA class I antibodies, only 20 demonstrated a clear positive FlowPRA. Class I FlowPRA of the other 12 patients with positive LSA appeared more likely to be negative. Among the 14 class II LSA positive patients, 7 patients’ FlowPRA appeared more likely to be negative. The majority of these HLA antibodies detected by LSA, but that did not cause a clear positive FlowPRA, had an MFI under 2000. A few of these antibody bindings were confirmed to be not reactive to antigens on cell surface in crossmatch. Conclusion The antigen density on LSA beads may be higher than on the FlowPRA beads which may explain that some antibodies may be detected by LSA but not FlowPRA. It could also not be excluded that some of the antibodies detected only by LSA might be non-specific which need further clarification. The clinical relevant of the weak antibodies detected only by LSA warrantees further studies. It is meaningful to test the HLA antibody using a combination of different detection platforms, especially for patients who will be transplanted using donors selected based on a virtual crossmatch.