Rapid Plasma Reagin Dx

Last updated: October 13, 2014

Synonyms: VDRL (venereal disease research laboratory) test, Wassermann test, reaginic antibody test.

Description: The RPR test detects antibodies that bind cardiolipin (so named because they were initially derived from cow heart). Historically, this test was of substantial importance because results were positive in patients with syphilis. Subsequently, a variety of tests and techniques were developed to check for reactivity to this antigen.

Method: The RPR test is a flocculation test (results may be determined macroscopically or microscopically).

Normal Values: RPR is not normally detected. (Negative results may be seen in early primary and late syphilis.)

Abnormal in: The RPR is sensitive but nonspecific.
—Syphilis: The sensitivity of RPR depends on the stage: 75% in primary syphilis, >99% in secondary syphilis, and 70% in late latent or tertiary syphilis. The diagnosis of syphilis is suggested by high or rising titers in the correct clinical setting. Alternatively, patients suspected of having syphilis may be assessed using a more specific test for treponemal infection, such as the FTA-ABS (fluorescent treponemal antibody absorption test) and MHA-TP. Patients positive for the RPR but negative for these treponema-specific tests are said to have a biologic false-positive RPR. Although not specific for syphilis, the RPR may be a prognostic aid in following the response to ther- apy because successful treatment of syphilis should be accompanied by re- version of the RPR to negative after a period of time (e.g., 1 year for primary syphilis).
—Other: Positive RPR results may be found in patients with a variety of other diseases, including mononucleosis, leprosy, hepatitis, SLE, and the APL syndrome.

Confounding Factors: False-positive results are seen in <2% of pregnant women.

Indications: The RPR test may be used to screen for primary or secondary syphilis in asymptomatic individuals with multiple sexual partners, to confirm the diagnosis of secondary syphilis in the presence of syphilitic lesions, to gauge efficacy of therapy, or to identify a biologic false-positive RPR.

Cost: $20–38.

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