From the Guidelines
Coombs' test is a crucial diagnostic tool used to detect antibodies or complement proteins attached to the surface of red blood cells, and it is strongly recommended in certain clinical scenarios, such as when a mother has not had prenatal blood grouping or is Rh-negative, as stated in the 2004 Pediatrics study 1. The test has two main types: the direct Coombs' test (DAT), which identifies antibodies already bound to red blood cells, and the indirect Coombs' test (IAT), which detects free-floating antibodies in the serum that can bind to red blood cells. Some key points about the Coombs' test include:
- It is used to diagnose autoimmune hemolytic anemia, hemolytic disease of the newborn, and to screen for compatibility in blood transfusions.
- The procedure involves mixing a sample of blood with Coombs' reagent (anti-human globulin), and if antibodies are present, the red blood cells will clump together (agglutinate), indicating a positive result.
- The test is named after Robin Coombs, who developed it in the 1940s, and it remains a fundamental diagnostic tool in hematology and transfusion medicine, as supported by its inclusion in diagnostic work-ups for various conditions, such as immune-related adverse events in patients treated with immune checkpoint inhibitor therapy, as recommended in the 2018 Journal of Clinical Oncology study 1.
From the Research
Definition and Purpose of Coomb's Test
- The Coomb's test, also known as the Direct Antiglobulin Test (DAT), is a diagnostic tool used to detect antibodies or complement proteins attached to red blood cells 2, 3, 4.
- The test is used to distinguish between immune-related and nonimmune acquired hemolytic anemia, and to diagnose conditions such as autoimmune hemolytic anemia (AIHA) and hemolytic disease of the fetus and newborn (HDFN) 2, 3, 5.
Clinical Applications and Interpretation
- The Coomb's test is widely used in laboratory medicine to identify situations where antibodies are bound to red blood cells, and to guide treatment decisions 4.
- The test can be used to detect antibodies against red blood cell antigens, such as those responsible for ABO blood group mismatch or Rh(D) incompatibility 3, 5.
- Interpretation of the Coomb's test requires careful consideration of the clinical context, as false-positive and false-negative results can occur 4, 6.
Limitations and Pitfalls
- The Coomb's test may not detect all cases of antibody-mediated hemolysis, particularly those involving low-affinity IgG antibodies or IgA alone 6.
- False-negative results can occur if the test is not performed correctly, or if the antibodies are removed during sample preparation 6.
- Alternative methods, such as flow cytometry or testing for IgA or IgM antibodies, may be necessary to detect cases of immune hemolysis not verified by the Coomb's test 2, 6.