Quote from klone
I'll do my best:
Coombs I'm a little less sure on. My understanding is that it measures whether there is the presence of a particular antibody (different from the D antibody that measure Rh, I believe) that can cause hemolysis in the current infant, which can cause hyperbilirubinemia. If an infant is indirect Coombs +, it means the infant is a "setup" for hyperbilirubinemia/jaundice, and the hospital staff will probably be more vigilant for signs of bilirubin, and have a lower threshold for treatment.
Just to clarify, there are 2 types of Coombs tests.
The Direct Coombs is done on the newborn's blood, and if positive, indicates an increased risk of hyperbilirubinemia, usually due to an Rh or ABO incompatibility between mother and baby. This has no bearing on administration of RhoGam.
The Indirect Coombs test is done on the mother's blood, and if positive, indicates that the mother has already
formed antibodies against the baby's positive Rh factor. In this case, a provider may choose NOT to give an injection of RhoGam, since it would be ineffective in preventing antibody formation. (Kind of like closing the barn door after the horse is already out.)
Fortunately, this is a rare scenario these days. Most Rh(-) women receive RhoGam prophylactically during pregnancy, or following a miscarriage or elective abortion, so sensitivity is rare prior to delivery. Because mixing of maternal and fetal blood can occur at delivery, an indirect Coombs test should be done on all Rh(-) mothers post-partum, and Rhogam given to mothers with a negative indirect coombs test to prevent sensitization that would potentially harm future pregnancies.