High negative predictive value of an amplified flow cytometry crossmatch before living donor kidney transplantation

Living kidney donation provides the advantage of assessing immunologic risk in detail before transplantation. It was our aim to analyze how results of an amplified flow cytometry crossmatch (FCXM) predict antibody-mediated rejection. T-cell-specific antibodies were analyzed in 92 donor/recipient pairs (164 datasets, average of 1.8 datasets per pair) with negative lymphocytotoxic crossmatch. FCXM results were expressed as delta values of the median fluorescence intensity (MFI), i.e., donor-specific MFI minus negative control. Based on receiver operating curve analysis, positive FCXM results were defined as delta MFI > 22. Delta MFI values in recipients with vs. without antibody-mediated rejection were significantly higher (n = 6 vs n = 86, p < 0.005). Recipients were grouped into those with reproducibly negative, varying, and reproducibly positive results (n = 69, n = 12, and n = 11, respectively). Only one of 69 patients with reproducibly negative results displayed antibody-mediated rejection, yielding a negative predictive value of 99%. Furthermore Fisher's exact test showed that the relative risk of a single positive FCXM result for antibody-mediated rejection is 10.1. Thus a negative T-cell FCXM before kidney transplantation is an excellent predictor of the absence of antibody-mediated rejection.