VDRL and TPHA: Blood Tests for Siflide

Generality

VDRL ( Veneral Disease Research Laboratory ) and TPHA ( Treponema pallidum Haemoagglutination Assay ) are two different serological tests, used for the diagnosis of the same disease: LA, better known as syphilis .

More precisely, VDRL and TPHA are screening tests ; as such, they are used to identify those individuals who most likely have contracted the disease but who need further tests for diagnostic confirmation.

VDRL and TPHA have a different clinical meaning, and are often performed jointly.

The TPHA has the disadvantage of being positive towards the tenth week of infection; as such, it is of little value in the early stages. It then tends to remain positive for life, regardless of therapy.

The VDRL is positivized between the eighth and fifteenth day after the appearance of the primary syphiloma (initial stage, which takes place after about three weeks of incubation, manifesting itself with a small painless wound that appears on the area where the infection occurred).

The VDRL, although a fairly sensitive exam, is scarcely specific. In fact, VDRL values ​​may appear high even in the absence of syphilis, for example in conditions such as pregnancy, autoimmune diseases (Lupus, rheumatoid arthritis), drug addiction and other viral infectious diseases (acute hepatitis, varicella, Epstein-Barr, measles) or chronic bacterial (leprosy, tuberculosis, malaria). As shown in the table, the sensitivity decreases in early primary syphilis and in latent and late congenital syphilis, phases in which it is around 75%; it is instead maximum (100%) in secondary forms. Since it becomes negative after adequate therapy, the VDRL is also used as a test to evaluate the effectiveness of the treatment.

What are

Syphilis is a disease caused by Treponema pallidum, a bacterium that is transmitted via the sexual route (acquired form) or through the placenta, if the pregnant woman is suffering from or contracting the infection during pregnancy (congenital form).

During acute infection, the subject shows the presence of specific antibodies against syphilis of the IgM type, followed later by the IgG type, which remain throughout life.

VDRL and TPHA are serological tests that involve the search for antibodies in the blood and sometimes in the cerebrospinal fluid (liquor).

• VDRL is a non-treponemic test, ie it is capable of detecting non-specifically directed antibodies against T. pallidum . This test is very sensitive, but not very specific: antibodies can be produced in the context of syphilis, but also in the presence of other diseases. In case of positivity, before making the diagnosis, another treponemic test should always be performed.
• TPHA is a treponemic test, capable of detecting specific antibodies directed against the T. pallidum antigens.

Because they measure themselves

VDRL and TPHA are used for research and diagnosis of Treponema pallidum infections.

These analyzes are indicated:

• As a syphilis screening: during pregnancy or following occasional highly risky sexual intercourse (multiple partners, habit of not using a condom etc.) or suspected exposure to the causative agent;
• In the presence of syphilis symptoms (such as genital ulcers, rashes, fever, fatigue, swollen lymph nodes, sore throat and muscle aches).

If the result of these serological tests is positive, further investigations should be performed for confirmation of active disease.

Normal values

Normally, the values ​​of VDRL and TPHA are negative, indicating that in all probability no infection is present; IgG and IgM are absent to indicate the lack of exposure to Treponema pallidum .

Warning! A negative result indicates that there is no evidence of the disease at the time of the examination. Recall that specific antibodies against syphilis are detectable only a few weeks after exposure to the pathogen. Therefore, if a person is certain that he has been exposed or if the suspect persists, the test is repeated after a few weeks.

VDRL and TPHA Alti - Causes

VDRL

VDRL values ​​typically appear high in the presence of syphilis.

However, these antibodies are not specifically directed against T. pallidum and can be produced by the body even during other diseases.

There is the possibility of incurring false positive results in the event of:

• Pregnancy;
• Autoimmune disorders (LES, Rheumatoid arthritis);
• Drug addiction;
• Other infections (including acute hepatitis, chickenpox, Lyme disease, measles, leprosy, tuberculosis and malaria).

Therefore, a positive result must be confirmed with the use of more specific tests.

If the patient is adequately treated, non-treponemal antibodies generally disappear after three years.

TPHA

• A positive TPHA result confirms the screening test result, then the diagnosis of syphilis.
• A negative result indicates, instead, that the VDRL exam had provided a false positive result and further tests are needed to investigate the causes.

How to measure them

For the execution of the VDRL and TPHA tests, a venous blood sample is taken from the arm.

Preparation

For VDRL and TPHA, no special preparation is required.

In some cases, a fast of at least 8 hours may be recommended, to prevent the food from interfering with the result. During this period, a small amount of water can be taken.

Interpretation of Results

VDRL and TPHA screening positive subjects must undergo a confirmatory test and quantitative antibody level assessment, with the triple aim of obtaining diagnostic certainty, assessing the degree of disease activity and laying the groundwork for monitoring of therapeutic efficacy.

Among the alternative or confirmation diagnostic tests we remember:

• the FTA-Abs test ( Fluorescent treponemal antibody absorption test - absorption test of fluorescent treponemal Ab), particularly useful in the initial stages (it is positive between the second and third day of the appearance of the primary syphiloma);
• the immunoblotting test (Western blot).

There are also immunological tests (Enzimatic Immunoassays, EIAs) for the detection of antibodies against syphilis. These tests are based on a series of recombinant treponema antigens, and can be used as confirmatory tests or replace the VDRL and TPHA pair for syphilis screening.

VDRL and TPHA in pregnancy

Screening tests for syphilis should always be performed during pregnancy. In this regard, pregnant women are divided into two groups, depending on the presence or absence of risk factors for the disease.

If these risk factors are present:

• 3 serological controls (VDRL - TPHA):
  1. at the first visit in pregnancy
  2. in the second quarter (28 weeks)
  3. at the time of delivery

if they are absent:

• 2 serological checks:
  1. at the first visit in pregnancy
  2. at the time of birth.