Background/Case Studies: A direct antiglobulin test (DAT) is used to evaluate hemolytic transfusion reactions and autoimmune hemolytic anemias. DATs are performed with polyspecific anti-human globulin (AHG, anti-IgG and –C3d), followed by differentiation between IgG and C3d using monospecific anti-IgG and anti-C3d. Evaluating RBCs for surface-bound C3d is traditionally performed using conventional tube test (CTT) methodology. A recently FDA-licensed DAT gel column agglutination card containing monoclonal anti-C3d reagent offers a new, more efficient method of detecting C3d on RBCs. As part of a large study evaluating the sensitivity of a DAT gel card, the data presented here compares the performance of CTT and gel methods in detecting RBC-bound C3d.
Study
Design/Methods: This IRB-approved study included 141 samples from 29 patients and 112 blood donors. Parallel testing between the gel method and CTT was performed at three sites: two used automated gel and one used manual gel. The FDA-licensed anti-C3 reagents chosen for CTT consisted of two murine monoclonal antibodies, anti-C3b and –C3d. Anti-C3d reactivity was considered the most reliable for comparison with the CTT method in a previous comparison study. Discordant sample results were tested by an independent fourth referee site.
Results/Findings: Of the 141 samples tested, the gel method demonstrated 100% concordance with CTT when tested with both manual and automated methods. The concordance of all test results was calculated by comparing the number of results in agreement (PPA+NPA, where PPA represents positive percent agreement and NPA represents negative percent agreement with the total number of results). 100% was achieved at all 3 test sites for PPA, NPA, and overall percent agreement (OPA). There was one discrepancy where the gel method result was consistent with the referee site. See Table 1. Conclusions: This study demonstrated that automated and manual anti-C3d gel card methods are substantially equivalent. As CTT monospecific DATs require time-consuming steps of washing RBCs, a gel method that includes polyspecific AHG, anti-IgG, and anti-C3d provides substantial efficiency and time-savings to transfusion services while maintaining accurate test results.
Importance of research: Blood banks are increasingly adopting automated gel testing systems. As automated gel systems harmonize immunohematology tests to one platform, efficiency and throughput improve turnaround time and reduce hands-on staff time in an ever-increasing resource-scarce environment. This research provides data to support that the detection of C3d on RBCs is equivalent to CTT. This method is currently the only FDA-approved gel methodology for automated performance of the monospecific DAT.
