Clinical and Interpretive

See Algorithm in Resources.  This test is used to determine the current disease status and to evaluate response to therapy for syphilis. It is also used in routine prenatal screening and as an aid in the diagnosis of active Treponema pallidum infection. Initially, depending on pregnancy status and age, either an RPR or an anti-syphilis IgG Ab test is performed. Depending on results, reflexive testing to fluorescent treponemal antibody absorbed (FTA-ABS) is performed.

Syphilis is a disease caused by infection with the spirochete Treponema pallidum. The infection is systemic and the disease is characterized by periods of latency. These features, together with the fact that Treponema pallidum cannot be isolated in culture, mean that serologic techniques play a major role in the diagnosis and follow-up of treatment for syphilis.

Patients with primary or secondary syphilis should be reexamined clinically and serologically 6 months and 12 months following treatment. Typically, rapid plasma reagin titers decrease following successful treatment but this may occur over a period of months to years.

Treatment response is generally indicated by a 4-fold (2-tube dilution) reduction in rapid plasma reagin (RPR) titer (eg, 1:32 to 1:8). For proper interpretation of RPR results, titers should be obtained using the same testing method and, preferably, at the same testing laboratory.

Failure of nontreponemal test titers to decline 4-fold within 6 months after therapy for primary or secondary syphilis might be indicative of treatment failure. Persons for whom titers remain serofast should be reevaluated for HIV infection.

This test algorithm can be used as a primary diagnostic approach for syphilis.

This test cannot be used for testing spinal fluid specimens.

Biological false-positive reactions with cardiolipin-type antigens have been reported in diseases such as infectious mononucleosis, leprosy, malaria, lupus erythematosus, vaccinia, and viral pneumonia. Pregnancy, autoimmune diseases, and narcotic addictions may give false-positives. Pinta, yaws, bejel, and other treponemal diseases may also produce positive results with this test.