Serologic testing: purposes of use

At the heart of all serological reactions is the interaction of antigens and antibodies. Serological reactions are used in two ways.

The first direction. Detection with the diagnostic purpose of antibodies in the serum of the subject. In this case, from the two components of the reaction (antibodies, antigens), the constituents of the blood serum are unknown, since the reaction is carried out with known antigens. A positive result of the reaction indicates the presence of antibodies in the blood that are homologous to the antigen used; a negative result indicates the absence of such. Reliable results are obtained by examining the paired blood serum of the patient taken at the onset of the disease (3-7th day) and 10-12 days later. In this case, it is possible to observe the dynamics of the growth of antibodies. In viral infections, only a fourfold increase in the antibody titer in the second serum is of diagnostic significance.

With the introduction of ELISA into laboratories, it became possible to determine in the blood of patients antibodies attributed to different classes of Ig (IgM and IgG), which significantly increased the information content of serological diagnostic methods. With the primary immune response, when the human immune system interacts with the infectious agent for the first time, antibodies attributed to IgM are synthesized predominantly. Only later, on the 8-12th day after the penetration of antigens into the body, IgG antibodies begin to accumulate in the blood. With an immune response to infectious agents, IgA antibodies are also synthesized, which play an important role in protecting against infectious agents of the skin and mucous membranes.

The second direction. Establishment of generic and species belonging to the microorganism. In this case, the antigen becomes an unknown component of the reaction. Such a study requires a reaction with known immune sera.

Serological studies do not have 100% sensitivity and specificity in the diagnosis of infectious diseases, can give cross-reactions with antibodies directed to antigens of other pathogens. In connection with this, it is necessary to evaluate the results of serological studies with great care and taking into account the clinical picture of the disease. This is due to the use of a variety of tests for the diagnosis of one infection, as well as the use of the Western-blot method to confirm the results of screening methods.

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