The role of the Coombs test in evaluating hemolysis in adults

Fig. 1: The direct antiglobulin test (DAT) and indirect antiglobulin test (IAT). AHG = antihuman globulin. A. The DAT reflects in vivo antibody sensitization of erythrocytes. Erythrocytes are washed to remove any unbound antibodies, and anti-IgG AHG reagent is then added. IgG antibodies cannot cause direct erythrocyte agglutination, but if the erythrocytes are coated with IgG antibodies, the AHG reagent will cause them to agglutinate. This test can also be performed using anti-complement AHG reagent. If IgG antibodies are present, they can be eluted off the erythrocytes for specificity determination. B. The IAT is used to detect the presence of IgG antibodies in serum (in vitro sensitization). Reagent erythrocytes are incubated in the presence of serum that potentially contains antibodies. If antibodies are present, they bind to their target antigens on the reagent erythrocytes. After the incubation period the erythrocytes are washed to remove unbound antibodies. Anti-IgG AHG reagent is added and will cause IgG-coated erythrocytes to agglutinate. Photo by: Lianne Friesen and Nicholas Woolridge.