Presently, the indirect immunofluorescent antibody (IFA) test using E. canis antigen is the most acceptable serological test. The presence of anti-E. canis antibody titers at a dilution greater than 1:40 is considered evidence of exposure. In the acute stage of the disease when dogs are clinically ill, antibody titers increase rapidly. At the time of presentation, clinically ill dogs in the acute stage of the disease have substantial antibody titers.