Koch test is a method for detecting tuberculosis in human blood before the onset of the acute stage, when the first characteristic signs of this disease occur. Initially, it was placed under the scapula, and it consisted directly of tuberculin - a substance that is the cellular material of dead tuberculosis bacteria.
The test result was evaluated after 48-72 hours by the manifestations of a local allergic reaction to a medication in the form of an infiltrate (subcutaneous densification), papule (swelling at the injection site, which is formed by immune cells producing antigens), as well as an increase in temperature and a marked deterioration in overall well-being.
The larger the size of the reaction to the Koch test, the greater the tuberculosis bacteria in the test person's body. The essence of such a test is a demonstration of the immune recognition of mycobacteria or its substances. A positive result indicated that these microorganisms are already present in the blood, and therefore, a person is either a carrier of an infectious pathogen or sick. If such recognition was not observed, it means that the person is absolutely healthy, and his immune system has not met with a tuberculosis bacterium.
About stick
Among the large number of mycobacteria, only two types are most dangerous for people - M. bovis and Koch's bacillus. Other types of infection are harmful only in immunodeficiency states or only animals are affected. In addition to species diversity, tuberculosis bacteria also have two forms: dormant and active. The sleeping form is a tuberculosis bacterium, covered with a special strong shell and penetrated into conditions where it can survive for many years, but it will not cause harm to its carrier.
Sleeping form
In a sleeping form, the tubercle bacillus is found almost everywhere, including in the body of most people. An awakened form of infection is an activated bacterium that can feed and multiply. It is precisely the main reason for the development of the pathological process. Koch's test for tuberculosis is able to respond to the presence of the causative agent of tuberculosis in the blood both in form and in appearance. Therefore, its positive result may not at all mean the presence of an active disease, but in most cases it shows a high tendency to it, which can occur after a decrease in the body's immune defense.
Indications for
The main indications for the Koch test are the presence of symptoms of tuberculosis, as well as diagnostic confirmation of the specialist's suspicions of the presence of the disease.
Below we consider how this study is conducted.
Statement technique
The Koch test algorithm for tuberculosis is quite specific. As for the dosage, there is no unequivocal opinion of doctors today. In pediatric practice, the test in most cases begins with 20 TE. To do this, 1 ml of purified tuberculin is introduced under the skin with classical dilution or 0.2 ml of the third dilution of purified dry tuberculin without preliminary studies of the threshold for sensitivity to this substance.
The first dosage of 20 TE for the Koch test is necessary if the Mantoux is of a normergic nature with 2 TE and a weakly positive or negative reaction to 100% tuberculin HCP. With such reactions at 20 TE, the dosage is increased to 50 TE, and then to 100 TE. In children with hyperergic reactions to Mantoux tests with 2 TE, the Koch test begins with the introduction of 10 TE.
Sensitivity Threshold Study
You also need to first know the threshold for sensitivity to tuberculin using Mantoux tests with different dilutions of tuberculin. Depending on this, threshold, suprathreshold and subthreshold doses of tuberculin are used for conducting Koch tests. For differential diagnostic purposes, suprathreshold dosages should be used, for example, at the 4th dilution of tuberculin, they are administered subcutaneously at a dose of 20-50 TE. To determine the small forms of tuberculosis, threshold dosages are used, i.e., a dose of subcutaneous tuberculin is administered 2-4 times higher than that established when determining intradermal titers.
Two days after the administration of tuberculin, the albumin-globulin coefficient significantly decreases as a result of a decrease in the content of albumin and an increase in α1-, α2- and 7-globulins.
Evaluation of the results
The results of a Koch test for tuberculosis can show the following:
- General reaction. At the same time, people feel worse, their body temperature rises (by about 0.5 degrees). As a rule, a rise in temperature is noted only on the second day after administration of the drug, somewhat less often by 4-5. The patient's blood counts are examined before the Koch stick test and after 48 hours. With tuberculosis, the number of leukocytes and ESR significantly increase, the number of lymphocytes and platelets decreases, and the albumin-globulin index decreases. With the genital form of tuberculosis, an increase in temperature is observed, the pulse becomes more intense, the level of stab neutrophils, lymphocytes, monocytes in the blood changes, ESR accelerates.
- Focal reaction. Violations are noted in the lesion. Sputum is examined in patients before and after the injection of the drug, X-ray monitoring is performed. A positive reaction, as a rule, is accompanied by an increase in symptoms and perifocal infiltration in the focal area. With the genital form of tuberculosis, pain appears in the lower abdomen, appendages become painful during palpation and swell.
- Local reaction. The Koch stick test is considered positive when an infiltrate is formed in a diameter of 1.5-2 cm. In the absence of other pathological symptoms, the local reaction to the sample is considered uninformative.
Body reactions
Koch tuberculin test can cause quite peculiar reactions of the body, one of which is tuberculin-eyed, which is characterized by reflex expansion of blood vessels in the fundus after a subcutaneous injection of tuberculin. A positive reaction of the sample is characterized by a significant expansion of blood vessels, staining of the boundaries of the disk and its hyperemia. With hypersensitivity under the influence of tuberculin in patients infected with tuberculosis, the proteolytic function of the blood increases. At the same time, relative hyperglobulinemia and hypoalbuminemia appear. Such changes, as a rule, are not observed in clinically healthy people or in people with tuberculosis in a state of normergia. With subcutaneous injection of tuberculin to a child, in most cases, a reaction develops in the form of hyperemia and the formation of infiltrate at the injection site. The diagnostic value of such a reaction is not always informative.