What is mixed with the patient's serum during the FTA-ABS test?

In the FTA-ABS (Fluorescent Treponemal Antibody Absorption) test, the patient's serum is mixed with killed Treponema pallidum, the bacterium that causes syphilis. This test is designed to detect antibodies specific to Treponema pallidum in the serum. The use of killed forms of the bacteria helps to ensure that the test is safe while still allowing for the detection of antibodies that the immune system has produced in response to an active or past infection.

The killed T. pallidum antigen provides a stable and standardized source for the test, enabling laboratory technicians to determine the presence or absence of those antibodies specifically associated with syphilis. This specificity is crucial for accurate diagnosis and is one of the distinguishing features of the FTA-ABS test compared to other syphilis screening tests that may not offer the same level of sensitivity and specificity.