Purpose of ABO and Rh Blood Type Testing in Newborns
The primary purpose of collecting ABO and Rh blood types in newborns is to identify potential hemolytic disease risk, particularly in cases of maternal-fetal blood type incompatibility, which can lead to significant morbidity and mortality if left undetected and untreated.
Key Indications for Blood Type Testing
Testing for ABO and Rh (D) blood types in newborns helps identify potential hemolytic disease of the newborn (HDN), which can cause anemia, hyperbilirubinemia, and in severe cases, kernicterus or death 1
When maternal blood is group O and Rh-positive, testing the cord blood for the infant's blood type and direct antibody test is optional but recommended for appropriate surveillance and follow-up 1
For Rh-negative mothers, cord blood testing for the infant's blood type and direct antibody test (Coombs' test) is strongly recommended to identify potential Rh incompatibility 1
Management of ABO Incompatibility
ABO incompatibility has become a more significant cause of hemolytic disease since the introduction of effective Rh(D) prophylaxis 2
Approximately 15-25% of all pregnancies are affected by ABO incompatibility, with varying degrees of clinical significance 3
In cases of severe ABO-HDN, exchange transfusion may be required to treat significant hyperbilirubinemia and prevent kernicterus 4
Newborns with blood group B born to mothers with blood group O may have higher risk of requiring transfusion (OR=2.9,95% CI 1.1-7.8) compared to group A newborns with O mothers 3
Management of Rh Incompatibility
For Rh-negative mothers who deliver Rh-positive infants, administration of Rh immune globulin within 72 hours of delivery is recommended to prevent maternal sensitization and reduce risk in subsequent pregnancies 5
The criteria for Rh immune globulin administration include: the mother must be Rh-negative and not already sensitized, and the child must be Rh-positive with a negative direct antiglobulin test 5
Without prophylaxis, Rh isoimmunization occurs in 12-13% of cases; with proper administration of Rh immune globulin, this risk is reduced to 1-2% 5
Laboratory Testing Protocol
The direct antiglobulin test (DAT or direct Coombs' test) on newborn blood samples is used to detect antibody-coated red blood cells, suggesting immune-mediated hemolysis 6, 7
Elution studies on DAT-positive samples can identify the specific antibody causing hemolysis (e.g., anti-A or anti-B in ABO incompatibility) 4
In cases of suspected hemolytic disease, additional laboratory tests include total serum bilirubin, complete blood count with reticulocyte count, and blood smear for red cell morphology 1
Clinical Implications and Monitoring
Newborns with positive DAT due to ABO incompatibility may require close monitoring for development of hyperbilirubinemia, with approximately 39% requiring treatment (primarily phototherapy) 2
Severe cases of hemolytic disease may require intensive phototherapy, intravenous immunoglobulin, or exchange transfusion if bilirubin levels approach or exceed exchange transfusion thresholds 1
The risk of kernicterus increases significantly when total serum bilirubin exceeds 25 mg/dL (428 μmol/L), making early identification of at-risk infants through blood typing critical 1
Prevention Strategies
Regular monitoring of Rh-negative pregnant women and appropriate application of Rh(D) prophylaxis is essential to prevent alloimmunization 8
For known cases of maternal sensitization, antenatal monitoring with middle cerebral artery Doppler studies may be indicated when antibody titers reach critical levels 6
Novel therapies such as intravenous immunoglobulin may be considered in high-risk pregnancies to prevent or delay the onset of severe fetal anemia 9