Independent Consultant - TSC Consulting Newtown, Pennsylvania, United States
Background/Case Studies: The direct antiglobulin test (DAT) has long been a valuable tool in the evaluation of the potential of hemolytic events in patients. The preparation of anti-human globulin (AHG) reagents has traditionally involved the use of anti-IgG and anti-C3 components produced in rabbits. Both rabbit sources for these antibodies require adsorption to remove unwanted heterospecific antibody. Switching to a mouse monoclonal (MM) source of C3 antibodies offers consistency of reactivity and minimizes cross reactivity. This performance study evaluated a polyspecific (PS) AHG reagent using MM anti-C3.
Study
Design/Methods: Four study sites compared the ID-MTS Gel™ Card Polyspecific (Anti-IgG;-C3d) formulated with rabbit anti-IgG and MM sourced Anti-C3b(clone F7G3)/Anti-C3d (clone C4C7) with a tube test based PS reagent BioClone® AHG Polyspecific Anti-IgG; -C3d (rabbit anti-IgG; MM C3-F7G3/C4C7) as the comparator. A referee tube test reagent PS AHG was used when discordant test results were encountered with a repeat test algorithm for concordance determination. There were ~1400 donor and ~1400 patient random samples tested across automated (Ortho Vision® Platforms (OV)), semiautomated (Ortho Optix™ (OP) Reader), manual gel (MG) and tube tests. As the result of a low number of positive DATs in the random samples, 205 (103 IgG and 102 C3) coated cells were prepared with varying concentrations of IgG antibody (anti-Fya or -D) or C3b or C3d and were tested. Statistical analysis of the test data employed overall agreement and lower bound 95% confidence interval (LBCI). Acceptance criteria were set at ≥95% at 95% LBCI.
Results/Findings: The overall agreement (OA) between the test polyspecific reagent and the comparator was 96%(OV), 98%(OP) and 98%(MG). See Table 1: Concordance Test Results and Discordant Analysis. The tube test, involved 137 positive DATs, of which 84 (61%), were positive in testing with the new gel reagent. The negative population of all tests was 8,273, defined by the comparator, of which 8,095(98%) tests were negative with the new gel reagent across the various systems. The prepared 205 DAT positive samples with IgG and C3 coating, demonstrated 100% concordance across all test systems, with reactivity ranges 1+ to 3+.
Conclusions: Occasionally, positive DAT reactions are encountered in random patient samples when DAT test are employed without clinical rationale. Variability of reactivity when comparing different test methods of different sensitivity is common for the DAT. Overall consistency in reactivity was seen in repeatable tests in discordant positive gel tests while tube tests demonstrated the inherent variability seen in manual tube. Overall, the ID-MTS PS Gel card performance characteristics met the acceptance criteria of 95% at a LBCI of ≥ 95%.
