Free antibody after low dose Rh immunoprophylaxis

Eighty Rh negative women delivering Rh positive babies were screened for red cell antibodies after their routine postnatal dose of 125 micrograms 7S anti D immunoglobulin. In all 80 free antibody could be detected. Distribution of titres by anti-human globulin (indirect Coombs) and ficin techniques were uninfluenced by ABO incompatibility, fetal cell counts, maternal weight or sampling time in the few days after immunoprophylaxis. Quantitations determined by autoanalyser showed some correlation with these variables. It is suggested that screening for free antibody is not the appropriate test to detect large fetomaternal spills which would warrant additional immunoprophylaxis.