Serum tests: the RPR and VDRL are sensitive but non-specific tests. Positive results may indicate active syphilis but confirmatory tests for specific antibody to T. pallidum are required. RPR or VDRL are also used for monitoring treatment.
The titre falls with successful treatment, but these tests may not become negative unless treatment is commenced early in the course of the infection.
Biological false positives may be found in pregnancy; transiently in eg, Measles, Chicken pox; chronically in eg, Cirrhosis, SLE, the Phospholipid antibody syndrome, Leprosy.
FTA-abs, TPHA: positive results confirm the diagnosis of syphilis, but do not indicate whether the disease is active, inactive or cured.
Titres may remain elevated after effective therapy, although they may become negative if treatment has been commenced early.
CSF examination: in the presence of positive serum tests the finding of one or more of an increased CSF white cell count, increased CSF protein, or positive VDRL supports a clinical diagnosis of neurosyphilis.
However, any or all of these CSF tests may be normal in the presence of neurosyphilis.
Direct detection of Treponema pallidum by nucleic acid detection after amplification (PCR) is available in some laboratories.