The Coombs test (synonym: Race-Coombs test) is an antiglobulin test named after the Cambridge pathologist Robert Royston Amos Coombs. It is used to detect incomplete antibodies (IgG) to red blood cells (erythrocytes).
One can distinguish a direct from an indirect Coombs test:
- The direct Coombs test (DCT) is used to detect incomplete antibodies bound to erythrocytes. For this purpose, the so-called Coombs serum is added to the patient’s erythrocytes. If the test is positive, the erythrocytes agglutinate (clump together).→ Detection of irregular antibodies on the erythrocyte membrane.
- The indirect Coombs test (ICT) detects non-bound incomplete antibodies circulating freely in serum (antibody search test). To do this, test erythrocytes are added to the patient’s blood serum, then washed again, and then test serum is added again. If the test is positive, agglutination then occurs.→ Detection of irregular erythrocyte antibodies in serum.
The procedure
Material needed
- 10 ml whole blood (no serum!)
Preparation of the patient
- Not known
Disruptive factors
- Not known
Indications – direct Coombs test
- Suspected transfusion incident – blood transfusion incident.
- Suspicion of haemolyticus neonatorum – fetal degradation of erythrocytes (red blood cells) due to blood group incompatibility between mother and child.
- Suspected autoimmune hemolytic anemia (AIHA) – occurrence of anemia due to the formation of antibodies directed against the erythrocytes.
- Positive self-sample in the indirect Coombs test.
Indications – indirect Coombs test
- Blood grouping (the indirect Coombs test is a component of any blood grouping).
- Maternity screening (4th – 8th SSW and 24th – 27th SSW).
- Suspicion of rhesus incompatibility (rhesus incompatibility).
- Suspicion of immunized persons (pregnancy; transfusions).
- Transfusions (esp. polytransfused patients).
- Suspected immunized patients (pregnancy,transfusions).
- Suspected autoimmune hemolytic anemia (AIHA) – occurrence of anemia due to the formation of antibodies directed against the erythrocytes.
Further notes
- Regular erythrocytic antibodies (anti-A, anti-B) are present in the blood when the patient is not himself a carrier of this blood group antigen. They are referred to as isoagglutins.
- Irregular erythrocytic antibodies are directed against other blood group antigens, most commonly rhesus D (anti-D).
