P047 A cold case: When single antigen beads assay do not respond

Abstract

Case history: We evaluated a live donor (D1) and recipient (P1) pair for potential kidney donation however their flow crossmatches (FXM) continuously result in B-cell positive. P1 was tested negative by single antigen beads and no donor specific antibody (DSA) was evident. Patient has been transfused once in 2014 and treated with adalimumab for ankylosing spondylitis in the past. Methods: Autologous FXM of D1 was conducted. A series of FXM with surrogate donors was conducted. Supplemental single antigen beads, FlowPRA beads and Luminex-based mixed screening beads were also conducted but results are questionable. Results: After the first allo FXM, a repeat was done to rule out B cell positive FXM whether it was reproducible. Since patient was screened negative by single antigen beads assay and supplemental beads, absence of DSA could not explain why B cell FXM can be positive. When patient serum subject to two other surrogate donors (D2 “O” and D3 “A”) interestingly B cell FXM has become negative. To rule out blood type issue and non–HLA factors, autologous FXM of D1 and allo-FXM with zero PRA serum (P2 “A”), and with positive PRA serum (absence of DSA, P3 “A”) were performed and all were found negative, but remained positive with diluted serum of P1. Patient P1 was tested again in 3 months however the same result remains. The final FXM was then focused on testing with surrogate donors (D4 and D5) who carry the same class II antigens as D1. The result became positive with D5. Although no clear evidence can confirm the antibody to DR11 to be allele specific, the collective results infer that suspected DSA DR11 is not distinguishable by FlowPRA screening beads and mixed beads and not detectable by single antigen and supplemental beads. Conclusion: This is the first case in our experience to discover such a situation with “cold bead” or specificity-unproven DSA. Transplantation is not recommended. Correlation between different assays and diligent testing to clarify unreasonable positive FXM is very important especially in cases of autoimmune disease.