(P-IG-20) Evaluation of a Gel Card Designed for the Detection of IgG and Complement

Background/Case Studies: The direct antiglobulin test (DAT) provides diagnostic support to the potential of immune hemolytic anemia. When diagnostic DATs are ordered, an initial polyspecific AHG DAT is common practice, followed by separate, monospecific tests for IgG and C3. Methods to perform DAT have varying levels of sensitivity and direct method comparison can expose this divergence. This performance study evaluated a gel card with reagents that separately test for the presence of IgG and C3 on patient and donor red cells.

Study

Design/Methods: The study compared a DAT breakdown gel card formulated with rabbit Anti-IgG, mouse monoclonal (MM) Anti-C3b,-C3d (clones F7G3 and C4C7) and a control in three separate microtubes with tube tests using rabbit Anti-IgG (ORTHO Anti-IgG reagent) and MM Anti-C3 reagent (BioClone^® Anti-C3b,-C3d) (MM C3-F7G3/C4C7) as comparators. Referee reagents, MTS™ Anti-IgG Card and Anti-C3d (ALBAclone^®) tube test were used when discordant test results were encountered along with a repeat test algorithm. There were 2,904 random patient and donor samples tested across automated (Ortho Vision^® Platforms (OV)), semiautomated (Ortho Optix™ (OP)), manual gel (MG) and tube tests at four sites. As the result of a low number of positive DATs in the random samples, 103 IgG (Anti-Fy^a or -D) and 100 C3b or C3d coated cells were prepared and tested.

Results/Findings: A total of 17,400 interpreted tests of random and contrived positive samples representing 26,506 microtubes were tested across the various test systems. The overall agreement (OA) between the test DAT card and the comparators was 99%(OV), 99%(OP) and 99%(MG) at the interpretation level. A 95% lower bound confidence interval (LBCI) was calculated for each test system. See Table 1: Individual Microtube Concordance – Random Patient/Donor Samples for individual microtube results. With referee/repeat testing of random positive sample discordants, IgG positive percent agreement increased 23-25% while C3 increased 17-19%. The prepared 203 DAT positive samples with IgG or C3 coating demonstrated 100% concordance across all test systems with reactivity ranges 1+ to 3+.

Conclusions: Discordant positive gel tests demonstrated consistency in reactivity upon repeat when compared to the variability observed in manual tube repeats. Positive DAT reactions are infrequent in random patient samples when a DAT test is employed without clinical rationale. Variability of reactivity is common for the DAT when using test methods with different sensitivities. Overall, the DAT breakdown card performance characteristics exceeded the acceptance criteria of 95% at a LBCI of ≥ 95%.