Treponema pallidum Antibody, IFA, CSF

Laboratory assay overview

This immunofluorescence assay (IFA) for T pallidum antibody, also called the fluorescent treponemal antibody absorption assay (FTA-ABS), may aid in the diagnosis of neurosyphilis. However, the preferred initial test for neurosyphilis evaluation is the Venereal Disease Research Laboratory (VDRL) test on cerebrospinal fluid (CSF) [1]. Neurosyphilis is a form of syphilis in which T pallidum invades the central nervous system [2]. The Centers for Disease Control and Prevention (CDC) recommends testing for neurosyphilis in syphilis patients with neurologic signs and symptoms and those with tertiary or ocular syphilis, using CSF and serologic studies [1]. No single laboratory test can diagnose neurosyphilis in all cases. CSF VDRL testing is specific, but not sensitive, for neurosyphilis. Therefore, if VDRL is negative in a patient with neurologic signs and symptoms, but there is serologic evidence of syphilis and an abnormal CSF cell count or protein result, additional testing with CSF T pallidum IFA may be useful. Neurosyphilis is very unlikely in patients with negative CSF T pallidum IFA results [1]. Treponema pallidum Antibody, IFA, CSF is a qualitative test (no titer is reported). Patients with a reactive result tend to continue to have reactive results throughout their lives, although some (15%-20%) treated during primary infection become nonreactive 2 to 3 years after treatment [1]. This test should be interpreted in the context of pertinent clinical and family history and physical examination findings. References 1. Centers for Disease Control and Prevention. MMWR. 2015;64:1-140. Accessed December 13, 2019. https://www.cdc.gov/std/tg2015/syphilis.htm 2. Tille, PM. The spirochetes. In: Bailey and Scott’s Diagnostic Microbiology. 13th ed. Maryland Heights, MO: Elsevier Mosby; 2014:535-539.