Direct addition of EDTA to LABScreen single antigen bead suspension: A simple way to prevent complement mediated interference and streamline HLA antibody testing.

Compromised detection of HLA specific antibodies due to complement mediated interference (CMI) is a well-recognized limitation of the single antigen bead (SAB) assay. Serum treatment with EDTA prior to SAB assay testing is a common strategy used to prevent CMI, however, treatment of individual sera, especially in large clinical runs, can extend assay turnaround time and increase the risk of a sample mix-up. In this study, we describe a simplified EDTA treatment strategy that can be applied simultaneously to all sera in a testing run. This strategy effectively prevents CMI without added pipetting steps and the increased turnaround time associated with other strategies. In the novel bead treatment (BT) method, EDTA solution and SAB suspension are combined and added into the wells of a testing tray together, patient sera are then added to the SAB/EDTA mixture. This eliminates the separate EDTA pre-treatment step used in the standard procedure (ST). Parallel testing using the BT, ST, and no EDTA treatment strategies followed by antibody identification using the Rapid Optimized SAB (ROB) protocol was performed for 19 well characterized sera with known CMI at two different laboratories. Both BT and ST methods were equally effective in preventing CMI. In addition, excellent MFI correlation was observed for specificities not affected by CMI. Both negative and pooled positive control sera performed as expected using the BT method and the pooled positive control serum, specifically designed to exhibit CMI, served well as an EDTA treatment control for all sera. The modified BT protocol can be easily implemented for clinical testing and eliminates extra pipetting steps, reduces the likelihood of pipetting error, and decreases turnaround time, while effectively preventing CMI and ensuring accurate detection of HLA antibodies. This protocol was recently implemented in the Halifax HLA Laboratory and has been very positively received by the laboratory team.