Influence of IgG subclasses on automated anti-D (Rho) quantification

Anti-D quantification by both an automated Polybrene method and an automated trypsin-albumin-dextran (TAD) method gave discrepant results in certain cases. These discrepancies, expressed as the polybrene TAD ratio of reactivity (PTR), were related to the IgG subclass of anti-D. Anti-D of the IgG3 subclass showed a higher PTR than IgG1 (0.94 vs 1.65). No difference was shown between G1m(1) and G1m(3) (0.93 and 0.95, respectively) or between G3m(11) and G3m(21) (1.40 and 1.81, respectively) allotypes. The simultaneous use of our automated Polybrene and TAD methods provides information about the anti-D subclass composition.