Historically, most hospital laboratories performed a blood type and direct antiglobulin test (DAT) on cord blood from all infants born to mothers who were either Rh negative or blood group O.

Six years ago, the American Academy of Pediatrics recommended 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 Hyper-bilirubinemia, Management of hyperbilirubinemia in the newborn infant 35 or more weeks of gestation. Pediatrics 2004; 114:297-316).

Following this recommendation, many laboratories nationwide stopped performing routine blood typing and DAT on babies that are born to Group O mothers because:

• ABO incompatibility seldom causes clinically significant hemolytic disease of the newborn
• Cord blood testing often produces falsely positive DAT results
• Strength of a positive DAT does not correlate with severity of jaundice that a baby might or might not develop

Recently, we reviewed the results of 795 cord bloods that were collected between September 1, 2007 and April 30, 2009. The data is summarized below.

This data provides additional evidence that cases of hemolytic disease of the newborn are not missed by the new policy. Only 10% of cord bloods had positive DAT and 40% of them occurred when the mom was Rh negative. This population is still tested under the new policy. None of the cases that had a positive DAT due to ABO incompatibility were associated with critically low hemoglobin or critically high bilirubin. The transfusion literature indicates that the DAT is not a reliable indicator of ABO HDN. A positive DAT is often associated with absence of hemolysis and yet hemolysis may occur with a negative DAT.  Monitoring of newborns for jaundice is best accomplished by measurement of bilirubin rather than a blood type and direct antiglobulin test.