In the fluorescent treponemal antibody-absorption (FTA-ABS) test, the patient's serum is first absorbed with an ultrasonicated suspension of a non-pathogenic treponeme before being applied to the antigen-coated slide. This step is performed primarily to:

• A Increase the sensitivity of the test for primary syphilis
• B Prevent the prozone phenomenon
• C Remove cross-reactive antibodies against non-pallidum treponemes ✓
• D Allow differentiation of IgM from IgG antibody

Explanation

FTA-ABS uses the Nichols strain of T. pallidum fixed on slides. Human sera contain antibodies against shared group antigens of commensal and saprophytic treponemes, which would produce nonspecific fluorescence. Absorption with sonicated Reiter treponeme removes these cross-reactive group antibodies, leaving specific anti-T. pallidum antibody to bind, thereby increasing specificity. Prozone relates to non-treponemal tests, and IgM differentiation requires the separate 19S-IgM-FTA-ABS modification.

Reference: Ananthanarayan and Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.