Прямой глобулиновый тест (ПАГТ)

The direct antiglobulin test (DAT) with polyspecific anti-human globulin (AHG)—also called the Direct Coombs test—assesses red blood cells for surface-bound immunoglobulin and/or complement. The assay is ordered when immune-mediated hemolysis is suspected and helps support the diagnosis of autoimmune hemolytic anemia by demonstrating in vivo coating of erythrocytes. When positive, follow-up with monospecific anti-IgG and anti-complement reagents clarifies the bound component.

Autoimmune hemolytic anemias arise when antibodies target red blood cell antigens, leading to destruction either within the circulation or in the reticuloendothelial system. Intravascular hemolysis typically reflects complement-mediated injury initiated by antibodies—most often IgM—forming a membrane attack complex; these are referred to as cold antibodies because they bind most efficiently at 4–18 °C. Extravascular hemolysis is driven by macrophage uptake of erythrocytes opsonized with IgG and/or C3 through Fc and complement receptors; such antibodies are termed warm and bind optimally at 37 °C. Laboratory detection leverages the presence of erythrocyte-bound immunoglobulin and complement as markers of immune hemolysis. Autoantibodies can behave as hemolysins (lyse cells) or as agglutinins (clump cells), and most detection strategies exploit in vitro agglutination. A contemporary approach uses gel agglutination: patient red cell suspension is added to microtubes containing gel impregnated with a polyspecific anti-human globulin reagent that recognizes IgG and C3 and may also react with IgA and IgM. After centrifugation, nonagglutinated cells traverse the gel and form a compact pellet at the bottom, whereas agglutinated cells are retained within or atop the gel, indicating coating by antibody and/or complement. A positive polyspecific DAT documents in vivo sensitization of red cells but does not identify the specific bound component. Characterization with monospecific reagents (anti-IgG, anti-IgA, anti-IgM, anti-C3, anti-C3b, anti-C3c, anti-C3d, and anti-C4) refines interpretation. The direct test detects only cell-bound antibodies; circulating antibodies may be present in serum and are assessed by the indirect antiglobulin test, which incubates patient serum with donor red cells before applying the same agglutination principle.