5-P

Abstract

In the recent years, luminex based Single Antigen Beads (SAB) analysis for HLA antibodies has acquired a fundamental role in predicting results for Flow (FCXM) and Complement Dependent Cytotoxicity crossmatches (CDC-XM). However, like any other technology SAB also has limitations. Here, we present report of a related kidney transplant where SAB failed to predict FCXM and CDC-XM result. A potential male kidney recipient was worked up for kidney transplant with his sibling. Patient was haplo-identical to his donor. Antibody testing showed Class I-/Class II+ antibody with weak DSA of DR11 and DQ5 at MFI of 1600 & 700 respectively. Unexpectedly, crossmatch was T cell negative and B cell positive for both FCXM and CDC-XM. To investigate this, we performed several additional investigations including serum dilution, dithiothreitol treatment, FCXM with surrogate cells FlowPRA specificity and investigation of patient treatment history for interfering substances. Treatment history of the patient showed no potential interfering event. Additional investigation including dilution of serum and treating with dithiothreitol did not reveal additional specificities or increase in the MFI of DSA. To rule out the contribution of non-HLA antibodies, patient serum was tested with FCXM against two different surrogate cells. First cell was DR11+/DQ5- and the second cell was DR11-/DQ5+. The FCXM results were consistent to DSA results for surrogate cells. Lastly, FlowPRA specificity on patient serum showed that all beads bearing DR11 are shifting to the right with 8 and 6 reaction strength. Luminex SAB is widely used to predict FCXM and CDC-XM results, SAB also has limitations in accurate prediction of XM results. We therefore recommend use of multiple techniques and platforms available to investigate and resolve discrepancies.