As explained earlier, today most labs do not use polyspecific antiglobulin serum for pretransfusion testing because the anti-C3 in polyspecific AHG can detect C3 bound by cold (clinically insignificant) antibodies such as anti-P1, anti-Lea, and harmless autoanti-I. However, polyspecific AHG can be useful to detect weak Kidd antibodies since they can bind C3. For example, a weak patient antibody may bind too few IgG anti-Jka molecules to the screen cells but lots of C3.
Figure 2-12 outlines the role of C3 in antiglobulin tests. The anti-C3 in polyspecific AHG serum consists of anti-C3b and anti-C3d. Anti-C3b detects C3b bound in in vitro tests. For (DATs), anti-C3d is essential to detect C3d which is bound in vivo. This is because, in vivo, C3b inactivators (which everyone has) have time to work. They cleave C3c from C3b and leave mainly C3d on the red cell.
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| Use polyspecific antiglobulin serum for (IATs) |