Test Detail
Interpreting Results

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Written by
Dr. Betina Chandolia
BDS, MDS - Oral Pathology and Microbiology
Reviewed by
Dr. Ashish Ranjan
MBBS, MD (Pharmacology)
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Rapid Plasma Reagin

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This test is for
Male, Female
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What is RPR/ VDRL?

The rapid plasma reagin (RPR) test is a blood test that looks for antibodies against a bacterial infection called syphilis. This test doesn't detect the actual bacteria that cause syphilis. Instead, it looks for antibodies against substances given off by cells that have been harmed by the bacteria.

It is used to screen for active syphilis infection and monitor response to treatment. Non-reactive RPR tests without clinical evidence of syphilis may suggest no current infection or an effectively treated infection. A false positive RPR (means positive results in the absence of syphilis) can be encountered in tuberculosis, malaria, and viral pneumonia. A reactive RPR test suggests past or present infections with the bacteria that cause syphilis. If not detected, syphilis can stay in the body for years and cause harm to internal organs.

Why is RPR/ VDRL done?

  • To screen for syphilis in people having symptoms of sexually transmitted infections
  • To screen people who are at risk of exposure to syphilis such as having another STD or HIV infection, homosexual men having a sexual partner diagnosed with syphilis, or indulged in high-risk sexual activity
  • To screen pregnant women for syphilis
  • To monitor the treatment of syphilis 

The treatment starts with antibiotics. With this, the level of syphilis antibodies fall and can be checked with another RPR test. Unchanged or rising levels can mean a persistent infection.

What does RPR/ VDRL Measure?

Syphilis is a sexually transmitted disease (STD), caused by the bacteria Treponema pallidum. It is most commonly spread by sexual route (through contact with syphilis sore (Chancre)). Syphilis is easily treatable with antibiotics. However, it can cause severe health problems if left untreated and can be potentially fatal. Maternal transfer to unborn child through an infected mother can cause serious and potentially fatal consequences for the baby.

There are several stages of syphilis:

·       Primary syphilis: Primary stage starts 2-3 weeks after being infected. It usually appears as one or more painless chancres on the sexual partner's chancre exposed body parts such as on the penis or vagina. Since it is painless, it may go unnoticed, especially if it is in the rectum or on the cervix. It usually disappears within 4-6 weeks even without any treatment.

·       Secondary syphilis: Primary syphilis can progress to secondary syphilis if the infected person is left untreated. The symptoms generally develop from 6 weeks to 6 months after the chancre first appears. It is mainly observed as non-itchy skin rash (rough, red, and spotted), appearing typically on the palms of the hands and the bottoms of the feet. Other associated symptoms could be fever, fatigue, swollen lymph nodes, sore throat, and body aches.

·       Late or tertiary syphilis: Secondary syphilis can progress to late or tertiary stage if it is further left untreated. In this, an infected person may remain without any symptoms (asymptomatic) but continues to have the infection and can last for years. There are various complications associated with tertiary syphilis which can occur if still left untreated such as the bacteria can damage the heart, eyes, brain, central nervous system (Neurosyphilis), bones, joints, or almost any other part of the body. Tertiary syphilis can last for years, with the final stage leading to mental illness, blindness, other neurological problems, heart disease, and death.

Interpreting RPR/ VDRL results


Negative: A negative ("non-reactive") RPR test result is compatible with a person not having syphilis.

The result of this test can be “positive” or “negative”. But there are some cases where the results can be false positive or false negative. 

A negative ("non-reactive") RPR test result suggests that a person is not having syphilis. However, the body does not always produce antibodies specifically in response to the syphilis bacteria, so the test is not always accurate. False-negatives test result may occur in people with early- and late-stage syphilis. Because of that other tests are required to confirm the results.

A false positive RPR (means positive results in the absence of syphilis) can be encountered in infectious mononucleosis, tuberculosis, leprosy, malaria, lupus erythematosus, vaccinia, and viral pneumonia. Pregnancy, autoimmune diseases, and narcotic addictions may give false-positive results. Also, this test may give false-positive result in pinta, yaws, bejel, and other treponemal diseases.

RPR test is also used to monitor treatment response. Treatment response is generally indicated by a 4-fold (2-tube dilution) reduction in rapid plasma reagin (RPR) titer (e.g., from 1:32 to 1:8). For proper interpretation of RPR results, titers should be obtained using the same testing method and, preferably, at the same testing laboratory.

Failure of nontreponemal test titers to decline 4-fold within 6 months after therapy for primary or secondary syphilis may be indicative of treatment failure. Patients whose titers remain serofast should be reevaluated for HIV infection.

Answers to Patient Concerns & Frequently Asked Questions (FAQs) about RPR/ VDRL

Frequently Asked Questions about Rapid Plasma Reagin

Q. Is there any risk associated with this test?
There is no risk associated with the test. However, since this test involves a needle prick to withdraw the blood sample, in very rare cases, a patient may experience increased bleeding, hematoma formation (blood collection under the skin), bruising or infection at the site of needle prick.
Q. What other tests are required for the diagnosis of syphilis?
There are other tests available that are required for the diagnosis of syphilis such as: 1. Antibody tests (serology): Antibody tests are most commonly used and they detect antibodies in the blood and cerebrospinal fluid (CSF). In this, there are two types of tests available for syphilis testing, nontreponemal antibody test and treponemal antibody test. Any of these two types can be used for syphilis screening, but it must be followed by a second test that uses a different method to confirm a positive result and to diagnose active syphilis. · Nontreponemal antibody tests—These are called "nontreponemal", as they detect antibodies that are not specifically targeted against the syphilis bacteria Treponema pallidum. Besides syphilis, these antibodies can also be produced in several other conditions (false-positive results). The tests are highly sensitive but are non-specific in nature. False-positive results can be seen in 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) and VDRL (Venereal Disease Research Laboratory) test. · Treponemal antibody tests: These blood tests detect antibodies that specifically target Treponema pallidum. They are highly specific for syphilis. However, once a person is infected and these antibodies develop, they remain in the blood for life. On the other hand, 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, TP-PA, and MHA-TP. FTA-ABS (Fluorescent treponemal antibody absorption) test is used to diagnose neurosyphilis. However, TP-PA (T. pallidum particle agglutination assay) test is sometimes performed instead of FTA-ABS because it is more specific and there are fewer false positives. MHA-TP (Microhemagglutination assay) test, another confirmatory method, is used much less commonly now. Immunoassays (IA): in more recent years, several automated tests have been developed, making them convenient for screening purposes. 2. Direct detection of bacteria—These tests are less commonly used now. Dark field microscopy is 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. 3. 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.
Q. What do you mean by false negative test RPR results?
False negative test results mean that RPR test is negative in the presence of syphilis infection. The body does not always produce antibodies specifically in response to the syphilis bacteria, so the test is not always accurate. False-negatives may occur in people with early- and late-stage syphilis. Hence, other tests are required to confirm the results.
Q. What do you mean by false positive RPR results?
False positive means positive results in the absence of syphilis. RPR test detects non-treponemal antibodies. This test is not specific for syphilis, although it is highly sensitive. A false positive RPR can be encountered in infectious mononucleosis, tuberculosis, leprosy, malaria, lupus erythematosus, vaccinia, and viral pneumonia. Pregnancy, autoimmune diseases, and narcotic addictions may give false-positives. Pinta, yaws, bejel, and other treponemal diseases may also produce false-positive results with this test.
Q. When is syphilis contagious?
Syphilis is most contagious during the first two stages and the early latent stage. It can spread through sexual route, therefore, it is known as sexually transmitted disease (STD). It can enter the body through the genitals, mouth, or broken skin. A pregnant woman infected with syphilis can pass it on to her baby.
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