Coombs’ Test – Part 3 – Hemolytic Anemia of Newborn, Rh-antibody, Anti-D Antibody
- The sample is serum from the mother.
- Whole blood (RBC) from the fetus or newborn.
- To diagnosis hemolytic anemia of newborn (HDN).
- To find out the presence of an Anti-D antibody in the serum of the mother.
- The red blood cells have various antigens on their surface which form various blood groups like Blood group ABO system and blood group Rh-systems (D-antigen).
- In the Rh-system, the Rh antigen is present on some of the RBC and those are called Rh-positive blood group while the RBC lacking Rh – antigens are called Rh-negative blood groups.
- There are a group of Rh antigens like Rh-C, Rh-D, Rh-E, and more.
- If the mother is Rh antigen (D-negative) and the baby is Rh antigen(D-positive), then because of the feto-maternal hemorrhage, the mother may be sensitized to Rh-antigen and develop Rh-antibody which are mostly IgG type antibody (anti-D antibodies).
- These maternal anti-D antibodies can cross the placental barrier, enters the fetal circulation, and leads to hemolytic disease of the newborn (HDN).
- Coombs’ test is used to detect antibodies in the Rh-negative mothers or in the newborn.
- Mother has free antibodies in the serum.
- Fetal/ newborn has coated RBCs by the antibodies.
- One can monitor the presence of the antibody during pregnancy.
- Indirect Coombs’ test is done to find a free anti-D antibody in the serum and is done on the maternal blood.
- A direct Coombs’ test is done to find RBC coated antibody in the fetus or newborn.
- Mother titer of more than 1:16 at 8th month indicates the presence of Anti – D antibodies in the mother. These can cross the placental barrier and enter fetal circulation.
- The fetus can develop hemolytic disease.