The antiglobulin (Coombs) test involves detection of a globulin bound to an erythrocyte using an antibody to that protein.
Terms:
(1) direct vs indirect
(2) temperature and thermal amplitude
(3) bound globulin (IgG, IgM, IgA, C3b, C3d, C4b, C4d)
Direct vs indirect
(1) direct: The protein is bound to a cell and antibody against the protein will cause agglutination.
(2) indirect: The protein is free in the serum and must become bound to a cell for agglutination to occur
Temperature and thermal amplitude:
(1) antibodies that bind optimally at low temperatures (typically 4°C) are called cold
(2) antibodies that bind optimally at body temperatures (37°C) are called warm
(3) some antibodies bind across a range of temperatures (from 4 to 37°C) and are referred to as having a broad thermal amplitude
Bound protein:
(1) IgG is typically associated with warm autoantibodies
(2) IgM and complement are typically associated with cold autoantibodies
(3) IgM antibodies that are reactive at temperatures greater than 30°C tend to be more clinically significant
