Serological tests of blood in the diagnosis of diseases

Serology is a section of immunology that studies the reactions of antigens to serum antibodies.

Serologic studies are a technique for studying certain antibodies or antigens in the blood serum of patients. They are based on responses of immunity. Widely apply these studies in the diagnosis of various infectious diseases and when determining the blood group of a person.

Who is assigned a serological examination

Serological analysis is prescribed for patients with suspected infectious disease. This analysis in contradictory situations with the diagnosis will help to establish the causative agent of the disease. Also, further treatment depends on the results of serological studies, since the determination of a specific microorganism contributes to the appointment of a specific treatment.

What material is being investigated

Serological studies involve taking biological material from a patient in the form of:

- blood serum;

- saliva;

- fecal masses.

The material should be in the laboratory as soon as possible. Otherwise, it can be stored in the refrigerator at a temperature of +4 or by adding a preservative.

Conducting the analysis

It is not necessary to prepare the patient specifically for the collection of these analyzes. Research is safe. Blood sampling is performed in the morning hours on an empty stomach, both from the ulnar vein, and from the ring finger. After sampling, the blood should be placed in a sterile, sealed tube.

Serological examination of blood

Human blood performs many functions in the body and has a very wide field of activity, and therefore there are many options for studying blood. One of them are serological tests of blood. This is a basic analysis conducted to identify certain microbes, viruses and infections, as well as the stage of development of the infectious process. Serologic blood tests are used for:

- determination of the number of antibodies against viruses and microbes present in the body. To do this, the antigen of the causative agent of the disease is added to the serum, after which the ongoing chemical reaction is evaluated;

- antigen determination by introducing antibodies into the blood ;

- determination of the blood group.

Serological blood tests are always prescribed twice - to determine the dynamics of the disease. A single determination of the interaction of antigens and antibodies only indicates the fact of infection. To reflect the full picture, where one can observe an increase in the number of links between immunoglobulins and antigens, a re-examination is necessary.

Serological tests: analysis and interpretation

An increase in the number of antigen-antibody complexes in the body indicates the presence of infection in the patient's body. Conducting specific chemical reactions with the growth of these indicators in the blood contribute to the definition of the disease and its stage.

If the result of the analysis shows the absence of antibodies to the pathogens, this indicates the absence of infection of the body. However, this happens rarely, since the appointment of serological analysis already indicates the detection of symptoms of an infection.

What can affect the result of the analysis?

You should closely monitor the conditions in which blood is taken. Do not allow anything in the blood to enter the bloodstream. The day before the analysis should not overload the body with fatty foods, alcohol and sweet drinks. It is necessary to exclude stressful situations and reduce physical activity. Biological material should be brought to the laboratory as soon as possible, as long-term storage of serum leads to partial inactivity of antibodies.

Serological methods of research

In laboratory practice, serological examination of the blood is complementary to bacteriological research. The main methods are:

1. Reaction of fluorescence, which is carried out in two stages. First, antibodies in the circulating antigen complex are detected. Then an antiserum is applied to the control sample, followed by incubation of the preparations. RIF is used for rapid detection of the causative agent of the disease in the test material. The results of the reactions are estimated using a fluorescent microscope. The character of the luminescence, the shape, size of the objects is estimated.

2. The agglutination reaction, which is a simple reaction of gluing discrete antigens with antibodies. Allocate:

- direct reactions used to detect antibodies in the patient's blood serum. A certain number of killed microbes is added to the serum and causes the formation of a precipitate in the form of flakes. Serologic studies on typhoid fever involve carrying out a direct agglutination reaction;

- Passive hemagglutination reactions based on the ability of red blood cells to adsorb the antigen on its surface and cause adhesion upon its contact with the antibody, and the precipitation of a visible precipitate. It is used in the process of diagnosing infectious diseases for the detection of hypersensitivity to certain drugs. When evaluating the results, the appearance of the sediment is taken into account. The precipitate in the form of a ring on the bottom of the tube indicates a negative reaction. Lace sediment with uneven edges indicates the presence of this or that infection.

3. Immunoenzymatic analysis, which is based on the principle of attaching the enzyme label to antibodies. This allows you to see the result of the reaction by the appearance of enzyme activity or by changing its level. This method of research has several advantages:

- very sensitive;

- Reagents used are universal, and they are stable for half a year;

- the process of accounting for the results of the analysis is automated.

The above listed serological methods of research have some advantages over the bacteriological method. These methods allow to determine the antigens of pathogens in a few minutes or hours. Moreover, these studies can detect antigens of the pathogen even after the treatment and the death of the bacteria that cause it.

Diagnostic value of the study

The results of serological studies are a valuable diagnostic method, but have an auxiliary significance. The basis for the diagnosis still remain clinical data. Serological tests are done to confirm the diagnosis if the reactions do not contradict the clinical picture. Weakly positive reactions of serological studies without a clinical picture confirming it can not be the basis for the diagnosis. Such results should be taken into account when the patient had a similar disease in the past and he underwent a course of appropriate treatment.

Determining hereditary signs of blood, confirming or refuting paternity, studying hereditary and autoimmune diseases, setting the nature and source of infection in epidemics - all this helps to identify serological blood tests. The interpretation of the results provides information on the presence of specific proteins to infections such as syphilis, hepatitis, HIV, toxoplasmosis, rubella, measles, typhoid fever.