Rprøve

Rprøve, or Rapid Plasma Reagin (RPR) test, is a non-treponemal serologic assay used to screen for infection with Treponema pallidum, the bacterium that causes syphilis. The test detects reagin antibodies that react with cardiolipin-lecithin-cholesterol complexes formed during tissue damage from syphilis. In practice, patient serum or plasma is mixed with the antigen-containing suspension; if reagin antibodies are present, visible flocculation or agglutination occurs, and the result is reported as reactive or nonreactive. If reactive, the antibody titer is determined by serial dilution.

RPR is primarily used as a screening test and to monitor treatment response, since reagin antibody levels tend to decline after effective therapy. It is typically followed by treponemal tests (such as FTA-ABS or TP-PA) to confirm active infection, because non-treponemal tests can yield false positives. The test is commonly utilized in pregnancy screening and blood donor screening, as well as in broader sexually transmitted infection workups.

Interpretation and limitations include several potential sources of error. False positives can occur with pregnancy, autoimmune diseases, certain infections, or medication use. False negatives may arise in very early primary infection or in late latent/tertiary syphilis. The RPR can also be affected by the prozone phenomenon at very high antibody levels, which may require sample dilution to reveal a true reactive result. Because the RPR is non-specific for Treponema pallidum, a confirmatory treponemal test is essential for a definitive diagnosis.

See also: syphilis testing, treponemal tests, non-treponemal tests.