VDRL (exam): what is it for? Positive, non-reactive and 1/2

What is VDRL?

VDRL is a blood test to diagnose syphilis . The non-reactive result indicates that the patient never had contact with the bacterium Treponema pallidum . A positive result may indicate that the patient has syphilis and the doctor will order other tests to confirm the diagnosis.

The test identifies the antibodies (defense cells) that the body produces to fight the disease and its early diagnosis is important to avoid serious problems at the brain and cardiovascular level.

It is not necessary for the patient to show symptoms for an exact result, which can be positive (reactive) or negative (non-reactive).

Individuals who have come into contact with syphilis carry antibodies to the bacterium for life. Therefore, the result will be positive even if the patient has already undergone treatment, but the concentration will be lower.

Because of this, the VDRL can also be a screening test, to make sure that the disease has been cured. With a lower number of antibodies, it is known that the infection is no longer active.

Attention !

The VDRL  does not  diagnose other sexually transmitted diseases (STDs).

How is the VDRL done?

This test is usually done through a common blood test, in which the health professional (a nurse, for example) ties a rubber band on the patient’s arm so that the blood vessels are wider and easier to find. That done, he inserts a needle into the vein and collects the blood, depositing it in a tube.

After the exam is performed, the professional places a gauze or cotton and a bandage over the place where the needle was, in order to stop any bleeding.

It is also possible to perform this test from a sample of spinal cord fluid: cerebrospinal fluid (CSF). In this case, the test is done in a hospital, where a healthcare professional takes a small sample of the CSF through a hollow needle that is inserted into the lower part of the spine.

After the exam, you should rest for at least 1 or 2 hours.

Preparation for the VDRL exam

It is recommended that the test be done after 4 hours of fasting, but this recommendation is not mandatory. If the blood sample is also used for other tests, the laboratory will make the necessary recommendations.

The exam result is usually ready in 7 days.

When should the exam be done?

A doctor can recommend this test when the patient has some signs and symptoms of the disease, such as:

  • A small, painless sore in the throat or genital area;
  • Swelling in the lymph nodes near the wound;
  • Rash that does not itch;
  • Visual changes in the throat or genitalia.

It can also be recommended, regardless of symptoms, when the individual:

  • He is undergoing treatment for another STD;
  • She is pregnant (the VDRL is a common exam during the prenatal period of pregnancy);
  • Had unprotected sex;
  • You have the HIV virus;
  • You have one or more syphilis-reactive partners.

VDRL on gravidez

The test should be performed at the beginning of prenatal care and be repeated in the second trimester of pregnancy, even if the first test has been negative. This is necessary during pregnancy as the disease can have serious consequences for the child, such as neurological problems.

If the test is positive, the pregnant woman will undergo treatment to eliminate the bacteria. If it is not followed correctly, the mother can transmit the disease to the baby through the placenta or the vaginal canal during delivery.

In positive cases, the pregnant woman should repeat this test monthly to confirm that the bacteria that caused the disease has been eliminated.

How to interpret the results of the VDRL exam

The effectiveness of the test will depend on the stage of the disease. The test is more sensitive to detect syphilis during the secondary stage. In the primary and latent stages, however, their sensitivity is lower. This can also end up causing flawed results, such as false negatives.

There is a more specific and sensitive test to diagnose syphilis: FTA-ABS . Such a test has a shorter immune window, which allows the disease to be detected after a few days of the onset of hard cancer. This test also has lower rates of false positives.

Knowing this, the results of the VDRL can follow different paths:

Non-reactive VDRL

When the result is negative (non-reactive), it usually indicates that the patient has never had contact with the disease-causing bacteria .

If the patient has already come into contact with the bacteria, it may mean that the treatment was completely effective, eliminating the bacteria and the antibody that fights it.

VDRL positive or reagent

If the result is positive (reagent), it may indicate that the patient has syphilis  , in which case the doctor may order a more specific test to confirm the diagnosis. If confirmed, it will indicate the correct treatment for the patient, usually done in a medicated manner.

VDRL reagent 1/2

The test result is given in dilutions and appears most commonly in titles, such as 1/2 and 1/64. These titles reflect the amount of treponemic antigens, that is, the amount of antigens against the bacterium Treponema pallidum  present in the patient’s blood: the higher the denominator (bottom), the greater the amount of antigens.

To understand the result, it is enough to know that the denominator represents the number of dilutions made in the blood. Therefore, if the result is 1/2, it means that it was possible to identify the antibody even after 2 dilutions in the blood.

This is the title does not characterize diagnosis. The result is characterized as a diagnosis only from values ​​greater than 32 dilutions, that is, 1/32.

False negative: prozone effect

It is called the prozone effect when the patient has syphilis and the test is negative. This occurs when the disease is in the latent stage, in which the infection is most widespread in the patient’s body.

False positive

Sometimes, the result is positive, but the patient has never had contact with the bacteria. This can occur when the body develops an antibody to other diseases, such as:

  • HIV;
  • Systemic lupus erythematosus;
  • Infectious mononucleose;
  • Hepatitis A;
  • Leprosy;
  • Malaria;
  • Some types of pneumonia.

Risks of the VDRL exam

The risks of examining blood samples are very rare . There is a possibility that, at the place where the blood was taken, a bruise or light bleeding may occur after collection.

Sometimes, too, the vein used for the examination may become swollen. If this happens, an ice pack, of a maximum of 20 minutes several times a day, can reverse the situation.

Individuals who use anticoagulant drugs or who suffer from clotting problems may experience continuous bleeding after collection. In this case, the patient must inform the professional of his condition before the examination.


Syphilis is a serious disease that needs to be treated quickly to avoid complications. Fortunately, with VDRL, this is possible in a quick and practical way, even during prenatal care.

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