PREVALENCE AND LACK OF CLINICAL-SIGNIFICANCE OF BLOOD-GROUP INCOMPATIBILITY IN MOTHERS WITH BLOOD TYPE-A OR TYPE-B

Purpose: To examine the prevalence and clinical significance of blood group incompatibility in infants whose mothers have blood type A or B. Methods: We prospectively analyzed cord blood samples from 4996 conse cutive live-born infants for blood type, hematocrit, and results of di rect antiglobulin (Coombs) test (DAT) and indirect Coombs test (ICT). Outcome measures: Erythrocyte sensitization was determined by positive DAT or ICT results. Significant hyperbilirubinemia (greater than or e qual to 224 mu mol/L (12.8 mg/dl)) and mean cord hematocrits were comp ared between mother-infant pairs with ABO incompatibility and positive DAT or ICT results and those with negative Coombs test results. Resul ts: Of all births, 6.9% (343/4996) were of infants who had ABO incompa tibility and had been born to mothers with blood type B or A; 44 (13%) of 343 infants had a positive antiglobulin test result, of whom 43 ha d a positive ICT result only. Type A or B mothers were 5.5 times less likely to have sensitization than type O mothers; A-B, B-A, A-AB, and B-AB mother-infant pairs with a positive antiglobulin test result had mean cord hematocrits and rates of significant hyperbilirubinemia simi lar to those of corresponding pairs whose antiglobulin tests both show ed negative results. Infants with a positive DAT result had lower mean cord hematocrits than infants with negative results on both antiglobu lin tests or on a positive ICT result only. Significant hyperbilirubin emia was more frequent in infants with a positive DAT result than in i nfants with negative results on both antiglobulin tests or a positive ICT result only. Conclusion: Sensitization is much rarer when the moth er has blood type A or B than when she has blood type O, as demonstrat ed by the antiglobulin test. The incidence of significant hyperbilirub inemia and lower cord hematocrit is not increased by sensitization whe n the mother has type A or B.