Direct fluorescent antibody
![Direct FA stained mouse brain impression smear reveals the presence of the bacterium Chlamydia psittaci. 400X.](/Images/godic/202501/09/Chlamydophila_psittaci_FA_stain5100.jpg")
A direct fluorescent antibody (DFA or dFA) (also known as "Direct immunofluorescence") is an antibody that has been tagged in a direct fluorescent antibody test. Its name derives from the fact that it directly tests the presence of an antigen with the tagged antibody, unlike western blotting, which uses an indirect method of detection, where the primary antibody binds the target antigen, with a secondary antibody directed against the primary, and a tag attached to the secondary antibody.