From the Research
An indirect Coombs test (Indirect Antiglobulin Test, IAT) is needed when screening for unexpected antibodies in a patient's serum, before blood transfusions, during pregnancy, and in the investigation of hemolytic disease of the fetus and newborn (HDFN). This test is essential before administering blood products to detect antibodies that could cause a transfusion reaction. It's particularly important for pregnant women to identify antibodies that might cross the placenta and affect the fetus. The IAT is also used in the workup of autoimmune hemolytic anemia and drug-induced immune hemolytic anemia.
Key Indications for IAT
- Screening for unexpected antibodies in a patient's serum before blood transfusions 1
- During pregnancy to identify antibodies that might cross the placenta and affect the fetus
- Investigation of hemolytic disease of the fetus and newborn (HDFN)
- Workup of autoimmune hemolytic anemia and drug-induced immune hemolytic anemia
Test Procedure and Interpretation
The IAT works by detecting antibodies that bind to red blood cells but don't cause direct agglutination. These antibodies are identified when anti-human globulin reagent is added, causing visible agglutination of sensitized cells. The test is typically performed as part of a pre-transfusion compatibility testing protocol, which includes ABO and Rh typing, antibody screening, and crossmatching. No special patient preparation is required for this test, and results are usually available within a few hours. However, it's worth noting that rheumatoid factor can interfere with the IAT and direct antiglobulin test, causing both false decreases and false increases 2.
Recent Recommendations
A recent study published in 2020 recommends routine indirect antiglobulin testing of all blood donors as a step to further improve blood safety 1. This study found that the incidence of unexpected antibodies among blood donors was 0.18%, highlighting the importance of screening for these antibodies to prevent transfusion reactions.