This document discusses the Direct Antiglobulin (Coombs) Test and Indirect Antiglobulin (Coombs) Test. The Direct Antiglobulin Test detects in vivo sensitization of a patient's red blood cells by antibodies and is used to investigate hemolytic disease of the fetus and newborn, transfusion reactions, and autoimmune hemolytic anemia. The Indirect Antiglobulin Test detects in vitro sensitization of reagent red blood cells by antibodies in a patient's serum and is used for full blood typing, antibody screening, and antibody identification. Both tests use antihuman globulin to detect antibody-coated red blood cells, but the Direct Test requires no incubation while the Indirect Test