What is VDRL / RPR?
Also Known As:
Venereal Disease Research Laboratory, VDRL, Rapid Plasma Reagin, RPR, Fluorescent Treponemal Antibody Absorption Test, FTA-ABS, Treponema pallidum Particle Agglutination Assay, TPPA, Microhemagglutination Assay, MHA-TP, Darkfield Microscopy, Automated Immunoassays for Syphilis Antibodies, Treponema pallidum by PCR
Syphilis Detection Tests
Syphilis is an infection caused by the bacterium Treponema pallidum that is most often spread by sexual contact, such as through direct contact with a syphilis sore (chancre), a firm, raised, painless sore. The most common syphilis tests detect antibodies in the blood that are produced in response to a T. pallidum infection. Some methods that are used less commonly directly detect the bacterium or its genetic material (DNA).
Syphilis is easily treated with antibiotics but can cause severe health problems if left untreated. An infected mother can also pass the disease to her unborn child, with serious and potentially fatal consequences for the baby. (See Common Questions below)
There are several possible stages with syphilis:
- Primary syphilis—the primary stage begins about 2-3 weeks after being infected. One or more chancres appear, usually on the part of the body exposed to the sexual partner’s chancre, such as on the penis or vagina. However, the chancre is usually painless and may go unnoticed, especially if it is in the rectum or on the cervix, and disappears within 4-6 weeks, healing regardless of whether the infected person is treated or not.
- Secondary syphilis—if primary syphilis is left untreated, secondary syphilis may occur from 6 weeks to 6 months after the chancre first appears. It is marked by a skin rash that often is rough, red, and spotted, appearing frequently on the palms of the hands and the bottoms of the feet (an unusual place for most other causes of rashes) and that usually does not itch. There may be other symptoms as well, such as fever, fatigue, swollen lymph nodes (“glands”), sore throat, and body aches.
- Late, tertiary syphilis—if untreated, secondary syphilis may continue into a latent stage, during which an infected person has no symptoms but continues to have the infection, and this stage can last for years. If still untreated, about 15% of people will develop the complications of late, or tertiary, syphilis. In these cases, the bacteria can damage the heart, eyes, brain, nervous system, bones, joints, or almost any other part of the body. When the central nervous system is affected, it is called neurosyphilis. Tertiary syphilis can last for years, with the final stage leading to mental illness, blindness, other neurological problems, heart disease, and death.
Syphilis is most infectious during the primary and secondary stages. In 2014, about one-third of over 63,000 new cases of syphilis reported to the Centers for Disease Control and Prevention (CDC) were primary or secondary stage syphilis. Eighty-three percent of these cases were among men who have sex with men.
Syphilis can be treated with antibiotics, preferably penicillin. Newly acquired infections can be cured easily; however, longer treatment may be needed for someone who has been infected for more than a year.
How is the sample collected for testing?
Depending on the stage of disease and test method used, different samples are needed:
Most often, blood is drawn from a vein in the arm to test for antibodies.
If a syphilis sore is present, a healthcare practitioner may take a scraping from the chancre on the affected area, such as the cervix, penis, anus, or throat.
If someone has late or latent stages of the disease with suspected brain involvement (neurosyphilis), the healthcare provider will perform a spinal tap to check the cerebrospinal fluid (CSF) for infection.
How is the test used?
Syphilis tests are used to screen for and/or diagnose infection with Treponema pallidum, the bacterium that causes syphilis.
Several different types of tests are available. Antibody tests are most commonly used.
Antibody tests (serology)—these tests detect antibodies in the blood and sometimes in the cerebrospinal fluid (CSF). Two general types are available for syphilis testing, nontreponemal antibody test and treponemal antibody test (derived from the name of the bacterium). Either type may be used for syphilis screening but must be followed by a second test that uses a different method to confirm a positive result and to diagnose active syphilis:
Direct detection of bacteria—these tests are less commonly performed:
- Nontreponemal antibody tests–these tests are called “nontreponemal” because they detect antibodies that are not specifically directed against the Treponema pallidum bacterium. These antibodies are produced by the body when an individual has syphilis but may also be produced in several other conditions. The tests are highly sensitive but, since they are non-specific, false-positive results can be caused by, for example, IV drug use, pregnancy, Lyme disease, certain types of pneumonia, malaria, tuberculosis, or certain autoimmune disorders including lupus. A positive screening result must be confirmed with a more specific (treponemal) test. Nontreponemal tests include:
- RPR (Rapid Plasma Reagin)–in addition to screening, this test is useful in monitoring treatment for syphilis. For this purpose, the level (titer) of the antibody is measured. It may also be used to confirm the presence of an active infection when an initial test for treponemal antibodies is positive (see below).
- VDRL (Venereal Disease Research Laboratory)–in addition to blood, this test is primarily performed on CSF to help diagnose neurosyphilis.
- Treponemal antibody tests–these blood tests detect antibodies that specifically target T. pallidum. They are highly specific for syphilis, meaning other conditions are unlikely to cause a positive result. However, once a person is infected and these antibodies develop, they remain in the blood for life. By comparison, nontreponemal antibodies typically disappear in an adequately treated person after about 3 years. Therefore, a positive treponemal screening result must be followed by a nontreponemal test (such as RPR) to differentiate between an active infection (or reinfection) and one that occurred in the past and was successfully treated. Treponemal antibody tests include:
- FTA-ABS (Fluorescent treponemal antibody absorption)–this test is useful after the first 3-4 weeks following exposure. In addition to blood testing, it can be used to measure antibodies to T. pallidum in the CSF to help diagnose neurosyphilis.
- TP-PA (T. pallidum particle agglutination assay)–this test is sometimes performed instead of FTA-ABS because it is more specific and there are fewer false positives.
- MHA-TP (Microhemagglutination assay)–another confirmatory method; this test is used much less commonly now.
- Immunoassays (IA)–in more recent years, several automated tests have been developed, making them convenient for screening purposes.
- Darkfield microscopy–this method may be used in the early stages of syphilis when a suspected syphilis sore (chancre) is present. It involves obtaining a scraping of the sore, placing it on a slide, and examining it with a special instrument called a dark-field microscope.
- Molecular testing (polymerase chain reaction, PCR)–this test detects genetic material from the bacteria in the sample from the sore, in blood, or in CSF.