The Diagnostic Automation Fluorescent Treponemal Antibody-Absorption (FTA-ABS) Test System is a
modification of the standard FTA-ABS test designed to confirm positive non-treponemal screen reagin tests for syphilis. The DAI. FTA-ABS test system employs nonviable T. pallidum (Nichols strain) cells as a substrate (antigen). The reaction occurs in two steps; (1)The substrate cells are reacted with specially treated patient sera in the first step. If the treponemal antibodies are present in the patient sera, an antigen-antibody reaction takes place between the substrate cells and the circulating anti-treponemal antibodies in the patient sera. (2)In the second step, goat anti-human immunoglobulin labeled with fluorescein isothiocyanate (FITC) is added to the T. pallidum substrate cells. The substrate cells are then examined with a fluorescence microscope. The intensity of staining is graded on a scale of 1+ to 4+ or as negative (no fluorescence).

Only freshly drawn and properly refrigerated sera, obtained by approved aseptic venipuncture procedures, should be used in this assay (16, 17). No anticoagulants or preservatives should be added. Avoid using hemolytic, lipemic, or bacterial contaminated sera. Sera should be stored at 2-8��C for no longer than 5 days. If delay in testing is anticipated, store test sera at -20��C or lower. Avoid multiple freeze/thaw cycles which may cause loss of antibody activity and give erroneous results.