is a treponemal test for syphilis
. Using antibodies specific for the Treponema pallidum
species, such tests are more specific than non-treponemal testing such as VDRL
. In addition, FTA-Abs turns positive earlier and remains positive longer than VDRL. Other treponemes, such as T. pertenue
, may also produce a positive FTA-Abs.
FTA (Fluorescent Treponemal Antibody) - Abs (absorption) should always be followed to confirm a positive RPR
test for syphilis. The ABS suffix refers particularly to a processing step used to remove nonspecific antispirochetal antibodies present in normal serum.
The antigen for the FTA-Abs test is whole bacteria. The bacteria cannot be cultured on laboratory media, so the organisms used are a lyophilized suspension of T. pallidum
extracted from rabbit testicular tissue. This is spread over and fixed to a slide. Patient serum is mixed with an absorbent (the "ABS" part of the test) containing an extract of a non-pathogenic treponeme, Treponema phagedenis
biotype Rieter. The purpose of the absorbent is to remove anti-treponemal antibodies that are not specific for the syphilis bacteria. The pre-adsorbed patient serum is then added to the slide; if the patient has been infected by syphilis, their antibodies will bind to the bacteria. FITC
(a fluorophore)-labeled anti-treponeme antibody and TRITC (another fluorophore)-labeled anti-human antibodies are added as secondary antibodies. The spirochete location is... Read More