RPR

Alternative names
Rapid plasma reagin

Definition

The RPR screening test is similar to the older VDRL test as both measure reaginic antibodies. These antibodies are usually produced during infection with syphilis as a result of the body’s interaction with the bacteria which causes syphilis (Treponema pallidum). This test is a useful screening tool for Syphilis, yet its ability to detect syphilis depends on the stage of the disease.

In the earliest stage of syphilis (primary syphilis) this test is positive approximately 60% of the time. The test’s usefulness increases with later stages of syphilis where it may be positive 70-90% of the time. In the final stages of syphilis, this test is usually positive in only 60% of cases.
There are several conditions which may cause a false positive test. These include HIV, lyme disease, mycoplasma pneumonia, Malaria and Systemic lupus erythematosus. This screening test, if found to be positive, must be confirmed by a more specific test for syphilis such as FTA-ABS.

How the test is performed

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to fill with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

Infant or young child:
The area is cleaned with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. A bandage may be applied to the puncture site if there is any continued bleeding.

How to prepare for the test
No special preparation is usually necessary.

Infants and children:
The preparation you can provide for this test depends on your child’s age, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following:

How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed
Syphilis is a highly treatable infection. In addition to screening individuals with signs and symptoms of sexually transmitted diseases, syphilis screening is a routine part of prenatal care during pregnancy. Several states also require screening for syphilis prior to obtaining a marriage license.

Normal Values

The value of a negative test depends on the stage of syphilis that is suspected. Screening test is most valuable in secondary and latent syphilis as it will most likely be positive during these stages. During primary and Tertiary syphilis this test may be falsely negative and additional testing may be needed prior to ruling out syphilis.

What abnormal results mean

A positive test result may indicate underlying syphilis. If the screening test is positive, the next step is to confirm the diagnosis with a more specific test for syphilis such as FTA-ABS. The FTA-ABS will distinguish between syphilis and other infections, including HIV, mycoplasma pneumonia, lyme disease, or autoimmune diseases such as Systemic lupus erythematosus.

What the risks are

     
  • Excessive bleeding  
  • Fainting or feeling light-headed  
  • Hematoma (blood accumulating under the skin)  
  • Infection (a slight risk any time the skin is broken)  
  • Multiple punctures to locate veins

Special considerations

The RPR test may be used not only for screening, but for monitoring the effect of antibiotic therapy for syphilis. After appropriate antibiotic therapy, the levels of reaginic antibodies should fall. Unchanged or rising levels can indicate persistent infection and may lead to additional medical evaluation.

Johns Hopkins patient information

Last revised: December 8, 2012
by Brenda A. Kuper, M.D.

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