Treponemal test TPHA (antibodies to Treponema pallidum), a marker of syphilis
Why this test?
For primary diagnosis of syphilis.
To evaluate the success of the treatment.
In what cases is it prescribed?
During a screening examination for syphilis. Pregnant women, blood (and organ) donors, representatives of certain professions (doctors, food workers, people in contact with children, patients before hospitalization or surgery) should be examined.
If syphilis is suspected (if the patient has symptoms of syphilis, genital ulcers or other sexually transmitted infections, as well as if his sexual partner has syphilis).
In particular, when a child was born to a mother suffering from syphilis.
After completing a course of treatment for syphilis.
The causative agent of syphilis is Treponema pallidum (pale treponema), a bacterium from the family of spirochetes. Syphilis is a venereal disease: it is most often transmitted sexually. In addition, it is possible to be infected through blood (for example, when sharing syringes, razors, etc.), the fetus from the mother or by household means (very rarely).
In the international classification of diseases, congenital, early and late syphilis, as well as unspecified forms are distinguished. In the medical literature, the concepts of primary, secondary and tertiary syphilis are used.
The incubation period begins from the moment of infection and lasts until the first symptoms (hard chancre) on average 21 days (from 10 to 90 days).
Primary syphilis is the stage from the appearance of a hard chancre to the appearance of a rash. A solid chancre is an ulcer that can appear in the place where the pathogen entered the body (usually on the genitals). It does not hurt and disappears (without treatment) after 2-6 weeks. Also, at the same stage, lymph nodes sometimes increase.
At first, the sick person remains seronegative (that is, there are no antibodies against syphilis in the blood yet). Secondary syphilis. Approximately 4-8 weeks after the appearance of chancre, new symptoms appear: a rash and general malaise, fever, headache, etc.
More severe manifestations are also possible. Then the signs of syphilis disappear and the disease enters the latent phase. At the same time, the causative agent still does not leave the body, therefore, when immunity is weakened, relapses of the disease may occur. Their symptoms coincide with the manifestations of secondary syphilis. It happens that syphilis remains in a latent form. But in some cases, if a person is not treated, tertiary syphilis develops over the years. At the same time, various organs and tissues are affected: the nervous and cardiovascular systems, bones, joints, etc. Serological tests (based on the detection of antibodies) are often used to diagnose syphilis. All types of tests can be divided into two groups: treponemal and non-treponemal tests.
Analysis for syphilis RPR refers to non-treponemal. Treponemal tests detect antibodies directed specifically against the T. Pallidum bacteria themselves, such as RPGA syphilis (passive hemagglutination reaction) or RIF syphilis (immunofluorescence reaction). With the help of non-treponemal tests, antibodies against cardiolipin (a lipid that is part of the membrane of mitochondria and bacteria) are detected. They appear in the human body from the stage of primary syphilis (about a week after the appearance of a hard chancre).
With non-treponemal methods of analysis for syphilis, the type of antibodies (IgG, IgM or others) is not taken into account, but the total response is determined. Such studies include precipitation microreaction: RPR, VDRL, etc. In primary and secondary syphilis, the sensitivity of non-treponemal tests is high (in the case of RPR: 86% in primary, 100% in secondary), and the higher the sensitivity of the method, the greater the probability that the test will detect the disease.
Accordingly, if a person has syphilis, the test result with 100 percent sensitivity will definitely be positive. However, when using non-treponemal tests, a false-positive result is also possible (detection of antibodies, despite the fact that the person does not have syphilis). The fact is that antibodies against cardiolipin occur not only in syphilis, but also in some other diseases. Therefore, when diagnosing syphilis, a non-treponemal test should be confirmed with a more specific treponemal test. Non-treponemal tests have another feature.
Antibodies against cardiolipin appear in the acute phase of the disease.
Therefore, when a person recovers, their level decreases, so that it is possible to judge the success of the treatment.