What Does it Mean if My Newborn Baby's Direct Coombs is Positive?

You may wonder what it means when you learn that your newborn baby has a positive direct coombs.

Well, the purpose of the direct coombs test (DAT) is to determine if there are antibodies attached to patient red cells.  In the case of newborn babies these antibodies would be antibodies from the mother.   This situation is called Hemolytic Disease of the Newborn (HDN) and it's dangerous for the baby because the antibodies break down the baby red cells, causing an increase in bilirubin. Elevated bilirubin levels in babies can cause brain damage and death if not monitored.

This can occur when the baby's blood type is incompatible with the mother's.  For example if the mother is type O, her natural Anti-A,B antibodies could attach to the baby's red cells if baby is type A. 

A more severe case is when the mother has an allo-antibody against a red cell antigen her baby has on its red cells.

 More babies used to die due to HDN but Rhogam and intrauterine transfusion help to reduce the severity of the situation.

Here is how we actually perform the direct coombs (DAT) in the blood bank.

1. We create a suspension of saline and baby red cells and wash a drop of it in a test tube.

2. Next we add Anti-IgG to the remaining red cells and centrifuge the tube.  If there is (mom) antibody attached to the baby red cells, the Anti-IgG will attach to these (mom) antibodies, causing the red cells to clump (agglutinate).  This would indicate a positive direct coombs test. 

3. We then would do a separate elution procedure to concentrate the attached (mom) antibody and identify it.