Red cell antibodies in pregnancy: there is no 'critical titre'.

The purpose of this study was to determine the predictive value and reliability of using a 'critical titre' when assessing the ability of red cell alloantibodies to cause haemolytic disease of the newborn. Titration studies and clinical follow-up of 418 antenatal cases where the mothers had red cell antibodies were studied retrospectively. The antibody specificities were anti-D (n = 359), anti-c (n = 34), anti-E (n = 19) and anti-K (n = 6). Depending on the titre being lower or higher than 16 in the indirect antiglobulin test, the severity of disease was established on the given therapy. Anti-D antibodies with a titre 16 were present in 20% of all cases associated with transfusion need of the child; for anti-c, -E and -K the figure was 4%. Titres > or = 16 resulted in both groups in 50% of the cases in phototherapy only, or no therapy at all. Titres are therefore not reliable indicators for predicting the severity of haemolytic disease of the newborn. Neither should they be used as a guide to whether or not antenatal intervention is indicated. Alternative quantitative or functional assays that measure cytotoxic lysis or phagocytosis or a combination of both should be performed instead.