Tuberculin test: significance, method and interpretation of results

Tuberculosis is a highly contagious disease caused by the microbial micobacterium tuberculosis. The source of infection is a sick person, animal or bacterial carrier.

In adulthood, infectiontubercle bacillus is almost 100%, but with sufficient level of immune defense, the disease does not develop. Also this good indicator is associated with the timely vaccination of BCG, which is first conducted in the first 3-7 days of the baby's life and is repeated in September of the first grade in school, and then in 14-15 years. However, it may also happen that the child will face a bacteriovirus and before the revaccination, and to detect this, a tuberculin test known to all as Mantou is intended. It is carried out annually, regardless of the results of the previous reaction, the only contraindication to it is hypersensitivity to the drug being administered. It is a hapten, i.e. defective antigen, prepared from inactivated mycobacterium tuberculosis. Tuberculin sample is injected intradermally into the middle third of the forearm, with a slight swelling, which is usually called a "button".

Interpreting the result

If the child has not yet been infectedmycobacteria, the reaction will be negative, and this tubercle will not change in color and size. In such a case, such a child will be revaccinated during adolescence. A positive tuberculin test is considered, if 72 hours after the injection of the drug infiltrate is equal to or more than 5 mm. In this case, it can be hyperemic or remain the same color. Also, the response to a tuberculin test may be questionable or hyperergic, with a more accurate assessment by a phthisiatrician. He also accepts children who have been diagnosed with tuberculosis, such patients are to be observed with him and treatment with special medications. To select schoolchildren for the revaccination of BCG, a tuberculin test is also used. Assessment of it is necessary, first of all, to determine the degree of immune activity of the body and protection from mycobacteria. The same is assessed when the vaccine is administered, that is, by the scar on the shoulder formed after BCG. In fact, the stronger the immunity of the child, the more pronounced will be the skin trail after it.

Sensitivity of the method

As the tuberculin sample is madeintracutaneously, it is quite sensitive to external factors. However, contrary to the widespread myth that it can not be drenched with water, it can still be done, only it is undesirable to use aggressive detergents, as well as rubbing the skin with a washcloth or combing it. All this can result in a false positive result. More sensitive, including water, is Pirke's scarification method by applying a skin scratch, which along with Mantou was performed earlier for the diagnosis of tuberculosis. However, at present it is used much less often.