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Animation description: The Antiglobulin Tests (also known as Coombs test). The direct antiglobulin test (DAT) is requested when immune-mediated hemolytic anemia is suspected. A blood sample must be drawn.
The patient's red blood cells may have antibodies (and other complement system factors) on the surface of some of the red blood cells (abbreviated as RBCs in this animation).
The blood sample is washed to remove the patient's plasma while leaving the red blood cells intact with their attached antibodies.
These red blood cells are incubated with anti-human globulin containing both anti-IgG and
anti-complement.
The anti-human globulin binds to the patient's antibody, coating the red blood cells, resulting in agglutination.
A positive DAT indicates that the red cells have been coated in vivo with immunoglobulin or complement and may suggest the presence of an
immune-mediated hemolytic process. The DAT is used in the investigation of transfusion reactions, auto-immune hemolytic anemia, hemolytic disease of the newborn and drug-induced hemolysis. Rarely the DAT may be positive in a normal individual.
To detect whether human anti-red blood cell antibodies are present in the plasma of a patient, an indirect antiglobulin test (IAT) is used.
Unlike the DAT which relies on the red blood cells in the sample, the IAT only deals with the extracted plasma.
Unbound human anti-red blood cell antibodies remain in the plasma.
The plasma is then incubated with reagent red blood cells selected to detect specific antibodies that are considered clinically significant.
The anti-red blood cell antibodies of the patient's plasma bind to reagent red blood cells to form antigen-antibody complexes.
The addition of anti-human globulin to these complexes results in agglutination of the red blood cells. A positive IAT indicates the presence of a red cell antibody in the patient.