Cord Blood Direct Antiglobulin Testing
Historically, many laboratories performed a blood type and direct antiglobulin test (DAT) on cord blood from all infants born to mothers who are either Rh negative or Group O. The American Academy of Pediatrics recommends ABO/Rh typing and DAT only on cord blood from all infants born to Rh negative women. (American Academy of Pediatrics Clinical Practice Guideline Subcommittee on Hyperbilirubinemia, Management of hyperbilirubinemia in the newborn infant 35 or more weeks of gestation. Pediatrics 2004; 114:297-316).
Nationwide, many laboratories have stopped performing DAT on babies that are born to Group O mothers because:
- ABO incompatibility seldom causes clinically significant hemolytic disease of the newborn (HDN)
- Cord blood DAT is often negative in cases of ABO HDN
- Strength of a positive DAT does not correlate with severity of jaundice that a baby might or might not develop
- Cord blood testing is unreliable & often produces falsely positive DAT results
- All mothers are instructed to see their pediatrician if signs of jaundice appear
The laboratory should store cord blood samples for 7 days so that a physician can order additional testing whenever there is clinical evidence of hyperbilirubinemia and or anemia. However, it should be noted that DAT testing on stored cord blood samples is unreliable and a fresh blood sample from the infant is recommended for optimal results.
In the absence of maternal alloimmunization during pregnancy, serological testing of infant blood may be necessary if the baby develops unexplained jaundice or anemia. Initial tests should focus on detecting ABO incompatibility between fetus and mother. An ABO and Rh type and direct antiglobulin test should be performed, even though the DAT is often negative in ABO hemolytic disease of the newborn. When ABO incompatibility exists, infant’s plasma can be tested for unexpected antibodies against reagent group O, group A1 and/or group B RBCs. The presence of maternally derived IgG anti-A or anti-B in infant’s plasma is sufficient evidence to support a diagnosis of ABO HDN.
