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Serological methods for laboratory diagnosis of syphilis. Serological tests Blood test for serological reactions

What does a serological blood test show? Diagnostic measures are the most important stage in the treatment of any disease. The success of treatment depends not only on the prescribed drugs, but also largely on how correctly the diagnosis was made.

In addition, diagnosis allows you to prevent complications and concomitant diseases. Using a serological test of the patient's blood, the presence of antibodies and antigens is detected. The study helps to find many diseases, determine their phase and monitor the progress of treatment.

What is serology?

Serology is the branch of immunology that studies the reactions of antigens to antibodies. This branch of medicine deals with the study of blood plasma and its immunological characteristics.

Today, a serological blood test for antibodies is a reliable way to detect human immunodeficiency virus, hepatitis, brucellosis, STDs and other life-threatening diseases. Let's figure out in what cases it is prescribed.

Indications for use

A serological blood test is necessary to identify the causative agent of the disease if it is difficult to make a diagnosis.

To carry out this reaction, antigens of pathogens are introduced into the plasma, and then the ongoing process is studied by a laboratory assistant. Or they carry out the reverse reaction: antibodies are injected into the infected blood to determine the specific identity of the pathogen.

Scope of application

This research is used in various branches of medicine. This reaction identifies specific cells and antibodies produced by the body to fight infections and viruses.

In addition, a person’s blood type is determined using the serological method.

A similar serological blood test is used in gynecology to diagnose sexually transmitted diseases. This method is also used for comprehensive examinations of pregnant women (detection of toxoplasmosis, HIV, syphilis, etc.). Passing this test is mandatory when registering with a antenatal clinic.

In children, a serological reaction is used to confirm the diagnosis of so-called “childhood” diseases (chickenpox, measles, rubella, etc.) if the symptoms do not have pronounced manifestations and it is impossible to identify the disease by analyzing clinical indications.

Detection of sexually transmitted diseases

For venereologists, this testing is truly irreplaceable and allows you to make a diagnosis very accurately.

With a blurred clinical picture, a serological blood test for syphilis, giardiasis, ureaplasmosis, chlamydia, herpes and other diseases can quickly detect the presence of antibodies.

Viral and infectious diseases

Serological analysis is actively used by gastroenterologists, hepatologists and infectious disease specialists to diagnose viral hepatitis.

Deciphering a serological blood test makes it possible to determine the stage of the disease and answer the question of how necessary hospitalization is at the moment. How to prepare properly?

Preparing for the test

Serological blood tests are done in both public and commercial clinics. Preference should be given to a laboratory with modern equipment and qualified personnel.

Biological samples for testing can be saliva and feces, but in most cases the patient's venous blood is used. Blood for a serological test is taken from the antecubital vein in a laboratory. Before taking the test, you should consult with your doctor about preparing for this procedure.

To prepare for a serological test, you need to follow a few simple rules.

Blood is donated in a calm state before meals, that is, on an empty stomach. Before this, you should not undergo other tests, such as x-rays, ultrasound, etc.

It is necessary to avoid taking antibacterial and some other drugs several weeks before donating blood. Certain recommendations in this case depend on the disease for which the test is being done. For example, a test for hepatitis involves eliminating fatty foods and alcohol 48 hours before the procedure.

Fluorescence reaction

Among the types of serological reactions there is a fluorescence reaction. This technique uses a reagent that illuminates antibodies in the blood serum.

Setting up a direct serological reaction involves marking specific antibodies with a fluorescent substance. This reaction is the fastest and is carried out in one stage.

Another option for conducting such an analysis is called indirect, or RNIF. It is carried out in two stages. In the first step, antibodies are not labeled with fluorescent tags, and in the second, appropriately labeled antibodies are used to identify antigens and antibodies. The glow occurs only after binding to a specific antibody occurs.

What does a serological blood test show? The result of the entire procedure is assessed by a special device that analyzes the strength of the radiation and reveals the shape and size of the object under study. The causative agents of infectious diseases are detected with a result whose reliability is 90-95%, depending on the type and stage of the pathology.

Enzyme immunoassay

These types of serological testing use unique, stable reagents. The marked substances seem to stick to the desired antibodies. As a result, we get a qualitative or quantitative result.

If no pronounced markers are found, the result will be considered negative. If the presence of antibodies in biological samples is detected during a qualitative study, then the test result is considered positive. By quantifying cells, the analysis gives a more accurate result.

By analyzing the analysis indicators (for example, the sum of identified cells), the specialist determines whether the disease is at the initial stage, in the acute stage, or whether the chronic form of the pathology has worsened. In order to make a diagnosis, the doctor takes into account not only the data of a serological study, but also the clinical picture of the disease.

Features of this test

Carrying out this analysis is not always able to provide 100% confidence that a certain disease has been detected. It happens that the results may be ambiguous and other procedures are required.

For example, during a test for brucellosis, blood serum is controlled for self-retention without antigen. This significantly increases the reliability of testing. A test for brucellosis can be positive or negative, and may also raise doubts.

If you receive questionable results that do not have an unambiguous interpretation, it is recommended to take the test again. In addition, brucellosis can be detected by blood cultures, bone marrow and cerebrospinal fluid examination.

Pros of serological blood test

Diagnostic techniques using serological reactions are widely used in modern medical practice. This is especially often done when determining viral and infectious pathologies.

The same tests are used during geographic screening and medical examination to prevent the epidemiological spread of infection.

The advantages of the method include:

  • High level of confidence.
  • Fast reaction and results. The results of the RSC are known within 24 hours. In a special situation, in a hospital setting, the analysis will be ready in a few hours.
  • Monitoring the development of the disease and the effectiveness of therapy.
  • Low cost and accessibility for patients.

Disadvantages of the method

However, serological studies also have their drawbacks.

These include the fact that when conducting an analysis, the incubation period of the disease should be taken into account in order to obtain a more reliable picture.

For example, determination of herpes simplex type 1 or 2 is possible only 14 days after infection. An analysis for the presence of the immunodeficiency virus is carried out 30 days, 90 days and six months after contact with an infected person.

Of course, the reliability of the results can also be influenced by the human factor: neglect of the rules for preparing for blood sampling or an error made by the laboratory assistant when carrying out the reaction.

According to statistics, an erroneous result can be obtained in 5% of cases. An experienced doctor, when examining a patient, having studied the clinical picture, in most cases can calculate the mistake made.

Serological research (tests)— laboratory research methods based on the detection of antibodies or antigens in the patient’s biological material. Most often, blood is used for analysis, less often - urine, saliva, purulent discharge or tissue samples taken during a biopsy.

Scope of application

  • Determination of blood group.
  • Identification of specific tumor proteins - tumor markers (for example, in case of suspected cancer of the ovaries, prostate, bladder, stomach, etc.).
  • Diagnosis of viral, bacterial, fungal, protozoal infections (HIV, syphilis, toxoplasmosis, chlamydia, rubella, herpes, helminthiasis, tick-borne encephalitis, etc.).
  • Determination of hormones, enzymes and drugs contained in the studied biomaterial in minor concentrations (less than 10−10 g/l).

The essence of the method is serological tests

Serological tests differ in the technique used, but they are all the result of the interaction of antigens (foreign compounds) with corresponding antibodies. The study consists of two successive phases. The first phase is characterized by the interaction between antigens and antibodies with the formation of immune complexes (positive reaction). In the second phase, external signs appear that confirm the presence of these same complexes (depending on the type of reaction, this may be cloudiness of the test solution, a change in its color, the loss of flakes, etc.). The absence of visible physical phenomena is regarded as a negative test result.

Preparation for serological studies

Depends on the type of research. A medical specialist should tell you about the specifics of taking a specific test when you sign up for the procedure.

You can take the necessary serological test at the Spectra clinic. We order analyzes from the best laboratories in the capital, working according to European standards, which guarantees fast and reliable results. Our doctors will help you decipher the conclusion and give recommendations for further diagnosis.

Table of contents of the topic "Methods for detecting viruses. Methods for diagnosing mycoses (fungal diseases). Methods for detecting protozoa.":










Detection of antiviral antibodies (AT) in blood serum. RTGA. RSK. REEF. Immunosorption methods for detecting antiviral antibodies.

A simpler and more accessible approach - detection of antiviral antibodies (AT) in serum. Blood samples should be collected twice: immediately after the onset of clinical signs and after 2~3 weeks. It is extremely important to examine exactly two serum samples. The results of a single study cannot be considered conclusive due to the inability to link the occurrence of AT to the present case. It is possible that these ATs circulate after a previous infection. In such a situation, the role of studying serum obtained during the period of convalescence can hardly be overestimated. The presence of the disease during the period of collection of the first sample is indicated by no less than a fourfold increase in the AT titer detected during the study of the second sample.

Methods listed below do not allow differentiation of antibodies(AT), formed during illness and circulating after recovery (the duration of this period varies for different infections). Since for adequate diagnosis it is necessary to confirm a significant increase in AT titers in two samples, the first sample is examined in the acute phase, and the second during the recovery period (after 2-3 weeks). The results obtained are retrospective in nature and are more suitable for conducting epidemiological surveys.

RTGA detects AT synthesized against hemagglutinins of viruses (for example, influenza virus). The method makes it possible to easily detect such antibodies (AT) in the patient’s serum.

RSK- basic method of serodiagnosis of viral infections(among those available). The reaction detects complement-fixing IgM and IgG, but does not differentiate them; To optimize the results obtained, staging the reaction requires certain personnel skills.

REEF. If it is possible to obtain a biopsy of infected tissue and the availability of commercial fluorescein-labeled AT kits, the diagnosis can be confirmed by direct immunofluorescence. The reaction involves incubating the tissue under study with AT, their subsequent removal, and fluorescence microscopy of the sample.

Immunosorption methods for detecting antiviral antibodies

Immunosorption methods(for example, ELISA and RIA) are more informative because they detect IgM and IgG separately, which allows one to draw certain conclusions about the dynamics of the infectious process or the state of convalescence. To detect AT, a known Ag is sorbed on a solid substrate (for example, on the walls of test tubes, plastic microplates, Petri dishes) and various dilutions of the patient’s serum are added. After appropriate incubation, unbound AT is removed, antiserum to human Ig labeled with an enzyme is added, the procedure of incubation and washing of unbound AT is repeated, and some chromogenic substrate (sensitive to the action of the enzyme) is added. Since the color change is proportional to the content of specific AT, it is quite possible to determine their titer spectrophotometrically. In the diagnosis of HIV infection, the immunoblotting method has found the most widespread use.

Infectious diseases initiate the production of appropriate antibodies in the blood of a sick person. This is how the body's immune defense works.

Determining the presence of antibodies to a specific virus or bacteria makes it possible to find out about the onset of a disease before its main symptoms appear. Today, serological tests provide the most complete picture. That’s why we’ll talk in this article about serological testing.

What are serological tests

Methods for studying biological materials of people and animals that can detect antibodies or antigens in them that the body produces as a protective reaction in the fight against infections are called serological studies. Such methods are used to determine the causative agent of infection, as well as for the purpose of:

  • determination of blood group,
  • studying immunity through determining the level of its humoral component,
  • determination of tissue antigens.

Who is it prescribed to?

Why do it?

The method is valued by specialists as a way to make a high-quality diagnosis of the disease.

  • If the patient is at the stage of the disease, then repeated studies are recommended to be carried out at intervals of approximately a week in order to monitor the effectiveness of the treatment used.
  • Serological tests are often used to determine which pathogen caused the disease after the patient has suffered it.

Types of procedure

Serological research methods are based on various reactions:

  • Neutralization reaction relies on the property of immune serum antibodies to act as a neutralizing agent against toxins or microorganisms themselves, preventing their damaging effects.
  • Agglutination reaction, which, in turn, is divided into the following subtypes:
    • direct reactions - they are used to test blood serum for the presence of antibodies. Killed microbes are added to the composition being studied, and if a precipitate appears in the form of flakes, it means that the reaction to this type of microbe is positive;
    • the indirect hemagglutination reaction is carried out by introducing into the blood serum erythrocytes on which antigens are adsorbed; These agents interact with the same kind of antigens present in the blood serum, resulting in a scalloped precipitate.
  • Reaction involving complement used to detect infectious diseases. The method is implemented through the activation of complement and observation of the reactions occurring in the medium under study.
  • Precipitation reaction is carried out by layering an antigen solution onto a liquid medium - immune serum. The antigen used for this method is soluble. The reaction is that the antigen-antibody complex undergoes precipitation; the resulting precipitate is called precipitate.
  • Reaction using labeled antigens and antibodies is based on the fact that microbes or tissue antigens, processed in a certain way, acquire the ability to emit light under the influence of ultraviolet rays. The method is used not only for diagnosing antigens, but also for determining medicinal substances, enzymes, and hormones.

Contraindications for

Due to the fact that the method involves studying the patient’s biological material, it cannot have a negative impact on humans. Therefore, there are no contraindications for use.

The study is completely safe.

We will describe below how a serological test is carried out.

Indications for testing

The method is used to determine the causative agent of infection, including for the following diseases:

  • HIV infection,
  • toxoplasmosis,
  • infectious diseases acquired through sexual contact;
  • diphtheria,
  • availability;
  • brucellosis,
  • staphylococcal infections,
  • hepatitis.

The method is also used to identify the following diseases:

  • opisthorchiasis,
  • amoebiasis,
  • cysticercosis,
  • giardiasis,
  • pneumonia.

Preparation for the procedure

No special preparations are required for the procedure. One condition must be observed: blood sampling is done on an empty stomach.

The algorithm for sampling (taking) blood (material) for serological testing is described below.

Carrying out analysis

Blood is drawn from the ulnar vein. In order for the study to work, blood is drawn not with a syringe, but by gravity. A needle without a syringe is inserted into a vein and up to 5 ml of blood is collected in a test tube.

During the procedure, the patient experiences slight discomfort as the needle is inserted into the vein. The subsequent steps are not at all worrying.

The interpretation of the results of a serological blood test is described below.

Decoding the results

The results obtained should be considered in conjunction with the clinical picture of the disease, checking the suspected diagnosis using several tests. This is due to the fact that the tests are specific and sometimes do not have absolute sensitivity to infectious diseases.

The price for a comprehensive serological blood test is described below.

Average cost of the procedure

The price of the procedure will depend on the type of study. It consists of the cost of the analysis and the cost of antibodies to a specific pathogen. The average cost of the procedure is within 700 rubles.

Serological reactions are described in the video below:

Unlike Trichomonas or gonococcus, Treponema pallidum cannot be detected in smears. If a person does not have obvious signs of the disease, then the best biological material for testing to diagnose syphilis is blood. A blood test for syphilis is quite reliable even when the patient has syphilides.

Do not be surprised if, during a medical examination before employment, surgery, or during pregnancy, you are asked to undergo a blood test for syphilis. This is a common procedure designed to screen the population. In this way, carriers of infection and patients are identified in the early stages.

Anyone who has had unprotected sex or suspects a partner of being a carrier may want to conduct a rapid diagnosis. Today it is possible to do testing yourself at home.

A blood test for syphilis is of particular importance in the process of treating an infection: based on the results, they judge the effectiveness of the chosen method of therapy and draw conclusions about the patient’s recovery.

A referral for analysis can be obtained not only from a venereologist-dermatologist, but also from a therapist, gynecologist or urologist. The analysis is done on your own initiative by purchasing a rapid testing kit at a pharmacy.

How to prepare for the procedure

To test blood for syphilis, in different cases, capillary or venous blood can be taken. Home rapid tests give the answer with one drop of blood from a finger. In this case, no special preparation is required. General recommendation: abstain from smoking immediately before taking a sample, and from alcohol for 24 hours.

Similar requirements are put forward when collecting venous blood. For patients with immunity problems, it is additionally not recommended to engage in heavy physical labor on the eve of tests. The day before taking samples, it is better to eat light food and get a good night's sleep.

Venous blood donation is carried out in the morning on an empty stomach.

Methods for searching for treponema or its traces

Laboratory methods for diagnosing syphilis by blood are based on the body’s ability to provide an immune response to the appearance of the pathogen. Since blood plasma or serum is studied, the entire group of reactions was called serological.

Serological diagnosis of syphilis includes non-treponemal and treponemal antibody tests. The former are more often used for screening and assessing the effectiveness of treatment, and the latter for diagnosis.

The first serodiagnosis of syphilis was carried out by August Wasserman in 1906. Until today, it has not lost its relevance and is called in honor of its developer - the Wasserman reaction (RW, RW) or the complement fixation reaction (RSK).

Laboratory practice has evolved significantly over 100 years, and IgM and IgG antibodies are now detected by the following methods (Table 1).

Non-treponemal reactions

The term “non-treponema” combines reactions that reveal antibodies not to the pathogen, but to the lipids of the destroyed membranes of the treponema or host cells. During the precipitation reaction, the reagent (cardiolipin antigen) interacts with antibodies (if any) and the antigen-antibody complex precipitates. White flakes form in the test tube. The laboratory technician evaluates the result with the naked eye in cases of RPR, MPR, RST and TRUST or under a microscope (VDRL, USR). The reaction is considered:

  • positive when large flakes appear (4+, 3+);
  • weakly positive when medium-sized flakes appear (2+, 1+);
  • negative – no flakes (-).

It can take up to 1.5 months from the moment of infection to a positive reaction in non-treponemal tests. Hard chancre manifests syphilis before the test by 1-4 weeks.

The titer of falling antibodies is measured during a quantitative precipitation reaction. To do this, plasma or serum is diluted according to the instructions. This analysis characterizes the effectiveness of treatment. If the titer drops, then recovery is successful; if the situation does not change, the medications should be changed.

When we talk about a microreaction, we mean that a few drops of the test material are required. Such tests are very convenient for screening large populations or performing at home. Test kits are cheap and come in a standardized form. For example, “Syphilis-AgKL-RMP” produced by EKOlab CJSC, “Profitest” from New Vision Diagnostics, SD BIOLINE produced by Standard Diagnostics.

The disadvantage of precipitation reactions is their low accuracy. RPR detects primary syphilis in the range from 70 to 90%, secondary - 100%, and late - 30-50%. False-positive results from nontreponemal tests are rare and occur in 3% of cases. An obstacle to obtaining accurate results may be errors in collecting or storing blood samples or violation of the order of analysis.

A positive precipitation reaction does not make a diagnosis of syphilis. To make a decision, specific treponemal tests are required.

Treponemal tests

Antibodies directly to treponema antigens can be detected in the patient's blood. For this purpose, specific serodiagnostic methods have been developed. Such tests are characterized by high sensitivity.

  1. Wasserman reaction

The most familiar and time-tested is the Wasserman reaction (WR) to syphilis. To carry it out, 5 ml of blood is taken from the cubital vein, serum is obtained from the sample, its own complement is inactivated, and then one part is treated with treponemal antigen, and the other with cardiolipin.

The result is assessed by the rate of hemolysis:

  • complete or significant delay in hemolysis – positive reaction (4+, 3+);
  • partial delay – weakly positive (2+);
  • minor delay – questionable reaction (1+);
  • complete hemolysis – negative result (-).

Positive qualitative results are cross-checked using a quantitative method. The reagin titer is considered to be the maximum dilution of blood serum until a complete or significant delay in hemolysis. A quantitative RT test is prescribed to evaluate the effectiveness of treatment.

It makes sense to carry out the Wasserman reaction 2-3 weeks after the appearance of chancre. It will show secondary syphilis in 100% of cases, tertiary syphilis in 75%.

  1. Passive hemagglutination reaction (RPHA)

The test preparation is prepared from animal erythrocytes by sensitization with Treponema pallidum antigen. The cells are added to the patient's blood serum. The test time is 1 hour. In the presence of antibodies, an agglutination reaction occurs, and the laboratory assistant sees specific patterns in the microwells.

Test transcript:

  • ring of agglutinated cells – positive result (4+, 3+, 2+);
  • loose ring – questionable result (+/-, 1+);
  • the dot in the center is a negative result (-).

The passive hemagglutination reaction gives positive results long after treatment. A false positive response can be obtained in cases of infection with leprosy or mononucleosis. Quantitative RPGA is carried out by diluting samples.

  1. Enzyme-linked immunosorbent assay (ELISA)

Used for early diagnosis of syphilis. Determines the presence of IgM, IgA, IgG antibodies to treponema using human immunoglobulins labeled with an enzyme and a special reagent. The answer is determined by the change in the color of the samples: the more antibodies, the more saturated the color of the mixture.

The method is very sensitive and specific. It does not give false positive results when patients are infected with other infections. High sensitivity to antibodies limits the use of ELISA to monitor the degree of cure.

  1. Immunofluorescence tests (RIF)

Analyzes in this group make it possible to quickly detect treponema infection before the appearance of chancre. Gives positive results by the end of the first week from the moment of infection. Sensitivity is close to 100%. The active ingredient of the test is fluorescein antibodies to human globulins. By combining with serum antibodies, they create luminous complexes. The test result is determined by the intensity of the glow:

  • yellow-green bright glow – 4+;
  • green – 3+;
  • pale green – 2+;
  • barely noticeable glow – 1+;
  • background coloring or shadows are negative.
  1. Treponema pallidum immobilization reaction (TRE)

The test is used to detect latent forms of syphilis. It is labor-intensive and technically complex. The technique is based on the phenomenon of immobilization of living treponemes by the “antigen + antibody” complex. Bacteria for the test are cultivated on rabbits. All glassware for analysis must be sterile. Blood is taken from the patient provided that he took antibiotics no later than a month before the day of the test. Treponemas are added to the serum. In the eyepiece of a microscope, a laboratory assistant looks for immobile bacteria.

Decoding the result:

  • if immobilization of treponemes is more than 50% - result 4+;
  • 31-50% – weakly positive 3+;
  • 21-30% – doubtful 2+;
  • up to 20% – negative.
  1. Immunoblot (Western-blot)

The most modern method for diagnosing syphilis, eliminating false-positive responses from other specific tests. In clinical practice it is used as a confirmatory test. The patient's blood serum is applied to a nitrocellulose membrane coated with electrophoretically separated Treponema pallidum antigens. If IgG and IgM antibodies are present, stripes appear on the test.

The results of the test system are interpreted based on the position of the bands and their intensity.

The final diagnosis is made taking into account non-treponemal and treponemal tests.

Sources:

  1. Akovbyan V.A., Prokhorenkov V.I., Novikov A.I., Guzey T.N. // Syphilis: Illustration. manual (Ed. V.I. Prokhorenkov). – M.: Medkniga, 2002. – P. 194-201.
  2. Dmitriev G.A., Frigo N.V. // Syphilis. Differential clinical and laboratory diagnosis. – M.: Med. book, 2004. – pp. 26-45.
  3. Loseva O.K., Lovenetsky A.N. Epidemiology, clinical picture, diagnosis and treatment of syphilis: A guide for doctors. – M., 2000.
  4. Novikov A.I. et al. Western blot as a confirmatory test in the laboratory diagnosis of syphilis. - “Wedge.” lab. Diagnostics", 2011, No. 8. – P. 4 -45.
  5. Pankratov V.G., Pankratov O.V., Navrotsky A.L. etc. // Recipe (appendix: International scientific and practical conference “Modern approaches to the diagnosis, treatment and prevention of sexually transmitted infections”, Grodno, 2005). – P.165-169.
  6. Pankratov V.G., Pankratov O.V., Krukovich A.A. and others // Healthcare. – 2006. – No. 6. – P. 35-39.
  7. Rodionov A.N. // Syphilis: a guide for doctors. – St. Petersburg: Peter, 1997. – P. 226-245.
  8. Jurado R.L. // STD. – 1997. – No. 3. – P. 3-10.
  9. Schmidt B.L. // First Russian Congress of Dermatovenerologists: Abstracts. scientific works – St. Petersburg, 2003. – T. II. – P. 40-
  10. Romanowski B., Sutherland R., Flick G.H. et al. //Ann. Intern. Med. –1991. – V. 114. – P. 1005-1009. What is serological diagnosis of syphilis