14-P

Abstract

Aim Single antigen bead (SAB) assay used to screen for anti-HLA antibodies also provides the mean fluoresnce intensity(MFI) that correlates with the strength/avidity of the HLA-Ab. Donor specific antibody(DSA) MFI values correlate well with actual crossmatch results and thus SAB is routinely used to perform virtual crossmatch. However, presence of interfering substances like IgM antibody, complement or medications, may result in false negative (FN) results. Recent studies have demonstrated that complement inhibition with EDTA decreases FN results. Additionally, manufacturer’s package insert states that EDTA plasma(plasma) is an acceptable sample for SAB. We present comparision of SAB results obtained from serum and plasma samples. Methods Serum and plasma samples from 11 patients were run in parallel using the Labtype Mixed beads (One Lambda, CA) on a Luminex platform. Number of antigens positive at cutoffs: 500-999, 1000-3999, 4000-7999, 8000-10000 and >10000 were compared. Results MFI values for positive control (PC) and negative control (NC) beads are decreased in the plasma and is reflected by higher PC/NC ratio for serum samples [ Table 2 ]. The total number of antigens identified at different cutoffs in serum and plasma are summarized [ Table 1 ]. Overall at lower cutoff there are more antigens identified in plasma, while at cutoff >8000 more antigens are identified in serum. Conclusions While the NC values are lower in plasma samples, there is a greater decrease in the PC values as reflected by higher PC/NC ratios in serum samples. In addition, this decrease in signal results in greater number of plasma specificities at lower cutoff. Clinical significance of these results need further evaluation.