VDRL test for syphilis

Medically Reviewed by Dr Sravya, MBBS, MS 


Syphilis is a sexually transmitted infection carried by the bacteria Treponema pallidum, and it is diagnosed by the Venereal Disease Research Laboratory (VDRL) test. Early identification of syphilis is essential since it can have major health effects if neglected. The body produces antibodies in reaction to the syphilis germs, which the VDRL test looks for. The laboratory checks a sample of blood for these particular antibodies. If the test is positive, syphilis antibodies are found in the blood, indicating either a recent or previous infection. 

vdrl test for syphilis

In order to confirm a syphilis diagnosis, additional testing is frequently required because false-positive results might happen.Syphilis can be harmful to both the sick person and their unborn child, so routine VDRL testing is crucial for people who are at risk for the disease, such as those who engage in sexual activity and pregnant women. Early detection enables prompt antibiotic treatment, stopping the spread of syphilis and its serious complications. 

Table of Contents

VDRL test meaning:-

The Venereal Disease Research Laboratory (VDRL) test is a blood examination used to identify antibodies the body produces in response to the syphilis-causing bacterium Treponema pallidum. It is a serological test that is frequently used to identify and track the development of syphilis infection. The VDRL test is explained in more detail below:


The main purpose of the VDRL test is to check for syphilis infection. Even if a person does not have any obvious symptoms, it can still be used to determine whether they have been exposed to the bacterium Treponema pallidum. Syphilis can advance through various phases and result in serious problems if untreated, thus early detection and control of the condition are essential.

How the Test works:

The VDRL test is a non-treponemal test, which means it recognises antibodies made by the body in reaction to the infection instead of the bacteria itself. In order to perform the test, a sample of the patient’s blood serum is combined with a solution that contains cardiolipin, a cellular component. Antibodies against Treponema pallidum in the patient’s blood will interact with the cardiolipin and result in observable clumping or aggregation. The amount of clumping is used to calculate the blood antibody concentration.


In most cases, the VDRL test results are presented in the form of clumps.  Indicating the dilution level at which clumping is noticed. Clumping was observed at a 1:8 dilution of the patient’s blood.


The more antibodies are found in the blood the higher the clumps availability occurs. While a declining number of clumps is successful therapy or previous illness, growing clumps may likely signify a present infection or treatment failure.


The VDRL test may at times yield false-positive findings because it is sensitive but not specific. False positives can also result from other situations such as some infections, autoimmune diseases, and pregnancy. Because it takes time for the body to create measurable levels of antibodies, the VDRL test may not detect syphilis in the very early stages of illness.


The Treponemal tests, which directly detect antibodies against Treponema pallidum (e.g., Fluorescent Treponemal Antibody Absorption or FTA-ABS), are typically conducted after the VDRL test if the results are positive or equivocal. Confirmatory testing helps in separating syphilis from other illnesses that could result in false-positive test findings.

It’s crucial to remember that only qualified medical personnel should administer and interpret the VDRL test. Go to a doctor for precise testing and diagnosis if you think you have syphilis or have been exposed to it

VDRL test for syphilis

Venereal Disease Research Laboratory (VDRL) Test:

The Treponema pallidum bacterium, which causes syphilis, stimulates the body to create antibodies, which are detected by the blood test known as the VDRL test. Because it is a non-treponemal test, it finds antibodies that react with things other than real bacteria. The test is utilised for syphilis infection screening and tracking.

How the Test Works:

Results of the VDRL test explanation:

Limitations and Considerations:

Due to conditions like autoimmune disorders, certain infections, pregnancy, and recent vaccinations, the VDRL test may yield false-positive findings.

– When antibody levels are not yet measurable in the early stages of infection, false negatives may occur.

– The VDRL test is a screening test, and to differentiate syphilis from other illnesses, it must be followed up with more focused testing, such as treponemal assays (e.g., Fluorescent Treponemal Antibody Absorption or FTA-ABS).

Follow-Up testing:

Doctors often conduct further tests to confirm the diagnosis and establish the stage of syphilis infection if the VDRL test is positive or unclear. These could include enzyme immunoassays (EIA), which directly detect antibodies against Treponema pallidum or treponemal diagnostics like the FTA-ABS test.

VDRL test reactive means

A positive VDRL test result means that the subject’s blood contains antibodies against the syphilis-causing bacteria Treponema pallidum. A reactive response, however, doesn’t offer precise details about the syphilis infection’s stage or if it’s active.

Reactive VDRL test outcome:

When a VDRL test yields a reactive result, it means that the immune system’s antibodies against Treponema pallidum have interacted with the test’s cardiolipin antigen, creating clumping or flocculation. This implies that the individual has had prior or ongoing exposure to the bacterium and that their immune system has generated antibodies against it.

Explanation and Considerations:

Clinical Importance

The reactive VDRL result provides an early signal that more research and assessment are required. This result will be used by medical specialists to determine the proper follow-up tests and, if necessary, potential treatments. Based on the findings of the tests and the clinical evaluation, the level of the syphilis infection will be assessed, as well as the best therapeutic strategy.


In conclusion, the early detection and diagnosis of syphilis, a sexually transmitted infection that can have major health repercussions, is greatly aided by the VDRL test. This test offers a reliable sign of syphilis infection by locating certain antibodies in the blood. It’s important to remember, too, that a positive VDRL result is not always indicative of an ongoing syphilis infection because false positives can happen. As a result, additional testing, such as the treponemal test, is frequently needed to confirm the diagnosis in cases when the VDRL test is positive. Early detection and treatment of syphilis are essential to halting the disease’s progression to more severe stages, which can harm many organs and bodily systems. In order to stop the spread of syphilis and protect the general public’s health, routine testing and safe sexual behaviour are crucial.