36-P : LUMINEX SINGLE ANTIGEN C1Q NEGATIVE,CDC POSITIVE HLA SPECIFIC ANTIBODIES

Aim Donor directed cytotoxic positive HLA antibodies have been associated with hyperacute rejection in solid organ transplantation. A potentially more sensitive new solid phase luminex single antigen –C1q assay is used as an adjunct to the CDC assay in detecting these cytotoxic antibodies. The aim of our study was to compare the binding of HLA antibodies in several assays: Luminex single antigen (LSA), LSA with diluted sera, C1q, enhanced C1q, and CDC assays to determine their accuracy, significance and relevance to Flow and CDC crossmatches Methods Sera from 39 recipients with multiple HLA class I and /or II antibodies by LSA were tested by LSA-C1q and CDC frozen panel assay. Enhanced LSA-C1Q assay using 4X serum volume and longer incubation time as well as flow and CDC crossmatch assays were performed on 5 samples that were CDC and/or flow positive and LSA-C1q negative. Results 72% of the time, the antibodies detected by the CDC assay was positive by LSA, LSA-dil tests, while 28% were positive by LSA and LSA-dil but negative by C1q. For two sera, negative LSA-C1q results were contributed by high background. The binding increased from negative/low positive by LSA-C1q to moderate/strong binding with enhanced LSA-C1q assay for 5 sera. The detection level of antibodies to DR15, DR16 and DR4 seemed to be problematic and had a low detection level by LSA-C1q assay but increased to positive by enhanced LSA-C1q assay. Conclusions sIn most cases LSA-C1q assay is efficient in identifying CDC+ antibodies. However there appear to be cases where the enhanced LSA-C1q and CDC assay detect antibodies missed by the C1q assay. Several test methods are required to determine the presence and function of HLA antibodies.