The fluorescent treponemal antibody absorption (FTA-ABS) test is a laboratory diagnostic procedure used to detect the presence of antibodies against the bacterium Treponema pallidum, which causes syphilis. This test utilizes a fluorescent conjugate to detect and visualize the interaction between patient antibodies and the treponemal antigen.
The test begins by first treating the patient's serum sample to remove any non-specific antibodies that may cause false-positive results. This is done by absorbing the sample with non-pathogenic treponemal cells. Any antibodies in the patient's serum that are specifically targeted against the treponemal antigen will bind to the absorbed cells, leaving the non-specific antibodies unbound.
Next, a fluorescent conjugate, typically containing fluorescein isothiocyanate, is added to the absorbed serum. If the patient's serum contains anti-treponemal antibodies, these antibodies will bind to the absorbed treponemal cells. The fluorescent conjugate will then attach itself to these antibody-antigen complexes.
In the final step, the sample is viewed under a fluorescent microscope. If the test is positive, a characteristic pattern of fluorescent treponemal cells will be observed, indicating the presence of anti-treponemal antibodies in the patient's serum. Conversely, a negative test result indicates the absence of specific antibodies against Treponema pallidum.
The FTA-ABS test is highly sensitive and specific, making it a reliable method for diagnosing syphilis. It is commonly used as a confirmatory test following a positive result with another screening test, such as the Rapid Plasma Reagin (RPR) test.
