Understanding Lab Tests for Hemolytic Disease of the Newborn (HDN)
Written by Private MD Labs Medical Writing Team • Last Updated: September 8, 2025
Hemolytic Disease of the Newborn (HDN), also known as erythroblastosis fetalis, is a potentially life-threatening blood disorder that occurs when there is a blood type incompatibility between mother and baby. The mother's immune system produces antibodies that attack and destroy the baby's red blood cells, leading to anemia, jaundice, and other serious complications.
Top Recommended Test
Rh Typing
This fundamental test determines whether a person has Rh-positive or Rh-negative blood. For pregnant women, knowing the Rh status is critical because if the mother is Rh-negative and the baby is Rh-positive, the mother's body can produce antibodies that attack and destroy the baby's red blood cells, leading to HDN.
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How Blood Tests Prevent HDN
While HDN develops during pregnancy or after birth, specific blood tests performed during pregnancy are the primary tools for identifying blood type incompatibilities and preventing this condition. Early detection through blood testing allows healthcare providers to monitor and manage potential complications before they become life-threatening.
Types of Blood Incompatibilities
HDN most commonly occurs due to Rh incompatibility (when an Rh-negative mother carries an Rh-positive baby) or ABO incompatibility (when a type O mother carries a baby with type A, B, or AB blood). Both scenarios can trigger the mother's immune system to produce antibodies against the baby's red blood cells.
Other Relevant Tests
Antibody Screen, RBC with Reflex to Identification, Titer, and Antigen Typing
This comprehensive test detects antibodies in the mother's blood that could destroy the baby's red blood cells, which is the underlying mechanism of HDN. The test also includes antigen typing to determine blood compatibility between mother and fetus, and measures antibody levels (titers) to assess the severity of potential risk.
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Know your blood type
This combined test identifies both the ABO blood group (A, B, AB, or O) and Rh factor (positive or negative). It's essential for detecting both ABO incompatibility (when an O-type mother carries an A, B, or AB baby) and Rh incompatibility, both of which can lead to the mother's antibodies attacking the baby's red blood cells and causing HDN.
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When Testing is Recommended
These blood tests are typically performed during early pregnancy as part of routine prenatal care. Early identification of blood type incompatibilities allows healthcare providers to monitor the pregnancy closely and implement preventive measures, such as Rh immunoglobulin injections for Rh-negative mothers, to prevent HDN from developing.
Important Considerations
The information provided here is for educational purposes only and is not a substitute for professional medical advice. Always consult with a healthcare provider for proper prenatal care, diagnosis, and treatment recommendations.
