Indirect Fluorescent Antibody (IFA), Treponema pallidum substrate
To confirm presence of Treponema pallidum antibodies in the diagnosis of syphilis.
The FTA-ABS should not be used to follow treatment or establish reinfection since specific treponemal tests may remain reactive for life. FTA-ABS test for syphilis has been reported to be falsely positive in patients with diseases associated with abnormally high globulin concentrations. In the absence of historical or clinical evidence of treponemal infection, a reactive minimal result (1+) should be considered equivocal.
Collect specimen in SST tube. Centrifuge; aliquot 1.5 mL of serum into 3 plastic vials (0.5 mL each), and refrigerate. Either Treponemal antibody FTA-ABS and RPR (FTA) or Treponemal antibody FTA-ABS only (FTA A) may be ordered. If FTA only is requested, results of non-syphilis serology (VDRL or RPR) must be indicated on requisition; 2 serum aliquots of 0.5 mL each are required for FTA only.
FTA-ABS is the most sensitive test in all stages of syphilis, and is the best confirmatory test for a serum reactive to a screen such as RPR or VDRL. FTA-ABS antibodies rise more quickly in primary syphilis and remain positive in tertiary syphilis. In late syphilis, approximately 1/3 of these patients may have a nonreactive VDRL or RPR. Therefore, if there is clinical suspicion of late syphilis and the VDRL or RPR is nonreactive, the FTA-ABS should be performed. This test is both sensitive and specific for syphilis infection. Less than 1% false positives are due to SLE, RA or old-age. All 1+ or minimally reactive results are considered equivocal; in the absence of historical or clinical evidence of treponemal infection, a second specimen should be submitted for serological testing.