rapid plasma reagin (RPR)

Indications

• syphilis
• pityriasis rosea*

* resembles secondary syphilis

Principle

• nontreponemal serologic tests used in the diagnosis of syphilis include:
  • VDRL reagin slide
  • rapid plasma reagin circle card (RPR)
  • unheated serum reagin (USR)
  • toluidine red unheated serum test (TRUST)
• all of these tests are based upon detection of immunoglobulin, IgG or IgM (reagin) directed against non treponemal antigens
• all nontreponemal assays utilize an active phospholipid (cardiolipin) antigen combined with lecithin & cholesterol in a colloidal particle

Clinical significance

Sensitivity (serum):

• primary: 77-100%
• secondary: 100%
• tertiary: 73%

False positives: (titers rarely exceed 1:8)

• connective tissue diseases
  • lupus erythematosus
  • rheumatoid arthritis
• infections
  • infectious mononucleosis
  • leprosy
  • malaria
  • Mycoplasma pneumonia
• pregnancy
• addiction
• some immunizations
• advanced age (10% of patients > 70 years of age)

Other antibodies found in patients with false + RPR:

• antinuclear
• antithyroid
  • anti-thyroid peroxidase
  • anti-thyroglobulin
• antimitochondrial
• rheumatoid factor
• Donath-Landsteiner antibody (paroxysmal cold hemoglobinuria)
• cryoglobulins

A positive RPR should be followed up with confirmatory testing:

• treponemal serologic test for syphilis

Methods

• antigen is mixed with charcoal in the RPR to make clumping of lipids by plasma antibody macroscopically visible
• the addition of choline chloride to the antigen eliminates the need to heat the serum before testing

Specimen

• serum, plasma
• RPR is NOT suitable for use with CSF

More general terms

• nontreponemal serologic test for syphilis
• reagin

Additional terms

• syphilis