When mothers with blood type O deliver babies who have blood types A or B, these infants often develop hemolysis, which places them at higher risk for hyperbilirubinemia. Approximately half of these will need phototherapy or other treatment for the elevated bilirubin levels. The Direct Antiglobulin Test (DAT), also known as the direct Coombs test, is used to detect the maternal anti-A or anti-B antibodies that have attached to the infant’s blood type A or B red cells, a sign of hemolysis. When the DAT is positive, it is assumed that the baby has increased levels of hemolysis of the red blood cells and is at higher risk for hyperbilirubinemia.
However, many hospital protocols do not screen for hyperbilirubinemia until after 24 hours of life, and a large proportion of newborns with hemolysis may require treatment before then. Dr. Michael Papacostas and colleagues at the Naval Medical Center Portsmouth and University of Pittsburgh conducted a retrospective study to determine if checking bilirubin levels early could predict the need for early phototherapy. The article describing their results, entitled “Sixth-Hour Transcutaneous Bilirubin and Need for Phototherapy in DAT Positive Newborns,” is being early released by Pediatrics this week (10.1542/peds.2021-054071).
The authors analyzed data from 772 infants who had positive DAT tests. Of these, one-third required phototherapy, and half of those requiring phototherapy required it in the first 24 hours.
A transcutaneous bilirubin (TCB) level done at 6 hours of age turned out to be highly predictive. If the level was lower than 3.0 mg/dL, it was 98% likely that the baby would not need phototherapy before 24 hours of life. If the level was 5.3 mg/dL or higher, it was 85% likely that the baby would need phototherapy before 24 hours of life. For those whose levels fell in between 3.0 and 5.3, the levels should be rechecked in 6-12 hours.
This paper is one that everyone who cares for newborns should read. It likely will change your practice regarding when you check bilirubin levels in babies with ABO incompatibility and a positive DAT.