51-P

Abstract

Aim Luminex based solid phase testing has become the assay of choice for detecting and identifying IgG HLA antibodies (Abs) and has become a key component in virtual crossmatching and a front line test for many transplant centers. Based on the strength (MFI values) of the donor specific HLA Abs, a patient is ruled in or out as the renal graft recipient. We address one of the existing challenges in the clinical use of Luminex platform as the screening tool; specifically, when low or negative HLA DSA by Luminex solid phase assay result is associated with a positive CDC XM result. We investigated whether EDTA treatment of sera unmasks the presence of IgG HLA Abs and provides a more accurate view of anti-HLA repertoire. Methods Representative sera were selected for the evaluation of EDTA treatment: Sera previously characterized to be Negative for anti-HLA; Sera previously characterized to be Positive for anti-HLA; Sera previously characterized to be Negative for anti-HLA by Luminex and positive by CDC, Masked sera. Two aliquots of each serum, untreated & treated with EDTA (5 μl EDTA/95 μl serum), were tested for HLA Abs using One Lambda Class I/II Single Antigen Bead assay. The trimmed mean MFI values were compared between untreated & EDTA treated samples. Results The major findings from our study were: 1) EDTA treatment of known Negative sera did not convert negative to positive results 2) EDTA treatment of known Positive sera did not convert positive to negative results; however some of the positive sera gave higher MFIs after treatment 3) EDTA treatment of sera previously found to be Luminex negative and CDC positive resulted in a substantive increase in the MFIs in the sera with low MFIs. Conclusions Our encouraging results advance the idea that EDTA treatment of serum may help resolve the paradox of low MFI with the donor HLA by the Luminex platform and positive CDC and FCXM results.