39-P

Abstract

Aim Low level antibodies may not always produce a positive flow crossmatch and increase the risk for transplant. The aim of this study was to investigate the impact of increasing the MFI cutoff for listing the unacceptable antigens (UA) in UNET. UA are use in virtual crossmatches and exlude recipients without performing crossmatches. Methods Antibody detection was performed by One Lambda LABScreen Single Antigen HLA Class I and II beads. The normalized MFI was used to calculate the cutoff. The MFI cutoff for a positive result was increased from 1,500 to 3,000. T and B cell crossmatches were performed by flow cytometry with pronase treated cells and reported as MCS. The T cell cutoff for positive was 61 and B cell was 93 which is 3 standard deviations above our negative control serum. The ten highest ranking recipients on the kidney runs from the first 8 deceased donor workups following the change were studied. Results Fifty six of the 126 actively listed patients from CTHH had UA entered in UNET. Low level UA were removed from 50/56 recipients. After the modification, eight recipients fell below and 21 stayed above 80% CPRA. The remainder had a CPRA range from 5-73%. 48 of the top 80 recipients on recent kidney match runs were from CTHH and further studied. 14/48 (29%) had low level antibodies present. 3/14 (21%) were flow T and B cell negative and the DSA was to DQ7 in all three crossmatches. Eleven were T and/or B cell positive. Four of the positive crossmatches were due to Cw, DQA, or DP antibodies which are not reported as UA. Three were due to low levels of multiple antibodies producing a cumulative effect. One was due to Bw6 antibody that reacted with all Bw6 beads on the Luminex assay but reacted below 3,000 MFI. The remaining four positive crossmtaches were due to historically higher MFI values. Conclusions Low level antibodies should not be added as unacceptable antigens and automatically rule out a recipient for kidney transplantation. Some crossmatches will be negative.