In the FTA-ABS test, what serves as the absorbent?

In the FTA-ABS (Fluorescent Treponemal Antibody Absorption) test, the absorbent used is a strain of Treponema pallidum, which specifically includes the Reiter strain. The purpose of employing an absorbent in this test is to eliminate nonspecific antibodies that may cross-react with the test antigens, allowing for a more accurate determination of specific antibodies against Treponema pallidum, the causative agent of syphilis.

While the other choices pertain to components or aspects of the test, they do not fulfill the role of the absorbent needed for the assay. The serum from the patient is what contains the antibodies being measured, while the Nichols strain of Treponema pallidum serves as a control antigen rather than an absorbent. A synthetic polymer is not appropriate in this context as it does not relate to the biological components of Treponema pallidum used in the test. By using the Reiter strain as the absorbent, the test enhances specificity and ensures that the results reflect true syphilis infections rather than false positives due to unrelated antibodies.