RPR

Definition

The RPR (Rapid Plasma Reagin) screening test measures antibodies called reagins that can be  produced by Treponema pallidum, the bacteria which causes syphilis.  However, the body does not always produce reagin specifically in response to the syphilis bacteria, so the test is not always accurate. The test is similar to the veneral disease research laboratory ( VDRL ) test. 

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. An elastic band is placed around the upper arm to apply pressure and cause the vein to swell 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.

In infants or young children: The area is cleansed 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 bleeding.

How to prepare for the test

No special preparation is usually necessary.

How the test will feel

When the needle is inserted to draw blood, you may feel moderate pain, or 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 screening test is most valuable in middle stage syphilis, as it will most likely be positive during this time. During early and late stage syphilis, the test may be falsely negative. Additional testing may be needed before 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 help distinguish between syphilis and other infections.

The RPR test's ability to detect syphilis depends on the stage of the disease. The test's sensitivity to detect syphilis nears 100% during the middle stages; it is less sensitive during the earlier and later stages.

The following conditions may cause a false positive test:

• HIV
• Lyme disease
• Certain types of pneumonia
• Malaria
• 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 can be used to diagnose syphilis and to see how well treatment is working. After appropriate antibiotic therapy, the levels of syphillis antibodies should fall. These levels can be monitored with another RPR test. Unchanged or rising levels can indicate persistent infection.

References

U.S. Preventive Services Task Force. Screening for Syphilis Infection: Recommendation Statement. Ann Fam Med 2004; 2: 362-365.

Illustrations

Blood test

Page Content:

Rapid plasma reagin ; plasma rapid reagin; plasma rapid reagin test