Blood Typing and Direct Antiglobulin Test (Coombs') Test
These are not screening tests but are appropriate in neonates in the following situations:
- When the mother is group O blood type
- When the mother is Rh-negative
- When the mother’s blood has an antibody that could be harmful to the baby
- When the baby has clinical symptoms that might be explained by the results of these tests
There are two main reasons to perform these tests on a newborn. The first is to determine if an Rh-negative mother should receive 'anti-D gamma globulin' after delivery. This treatment helps prevent the development of
antibodies in the mother that could be harmful to a baby in future pregnancies. Only Rh-negative mothers of Rh-positive infants receive the treatment.
The second reason to perform these tests is to identify newborns that may be at risk of anaemia due to harmful antibodies from the mother's blood. For example. babies with either group A or B blood type may react with antibodies produced by mothers with group O blood type. A direct antiglobulin (Coombs') test is used to determine if the mother’s antibodies have reacted with the baby’s blood cells.
A negative test usually means that the mother’s antibodies are not affecting the baby’s blood and the infant is not at risk. A positive test means the baby is at risk of developing anaemia. Many reactions to maternal antibodies produce only mild symptoms in the newborn. Some reactions, however, can cause moderate to severe anaemia, brain damage and death.
A positive direct antiglobulin test does not necessarily mean the baby will develop anaemia.
