Coombs Test

Excerpt

Antiglobulin testing, also known as the Coombs test, is an immunology laboratory procedure used to detect the presence of antibodies against circulating red blood cells (RBCs) in the body, which induce hemolysis. The destruction of these red blood cells (RBCs) by antibodies directed against them is described diagnostically as autoimmune hemolytic anemia (AIHA). Many etiologies fall under this classification.

Antiglobulin testing can be either direct antiglobulin testing (DAT) or indirect antiglobulin testing (IAT). The principle of DAT is to detect the presence of antibodies attached directly to the RBCs, which takes place by washing a collected blood sample in saline to isolate the patient’s RBCs; this procedure removes unbound antibodies that may otherwise confound the result. IAT, by contrast, is used to detect unbound antibodies to RBCs, which may be present in the patient’s serum. Direct antiglobulin testing adds a monospecific or polyspecific reagent to the washed RBCs to detect bound IgG and/or complement C3. In practice, many laboratories first use the polyspecific reagent that can detect both IgG and C3; a positive result is followed by monospecific testing to characterize the antibody further. For indirect antiglobulin testing, serum from a blood sample gets isolated, and native RBCs are removed. The isolated serum sample then gets incubated with foreign RBCs of known antigenicity. Antiglobulin reagent is then added, and the presence of agglutination indicates a positive result.