How much is pcr done for latent infections. How PCR analysis is carried out: a description of the procedure. If a smear is given, it is necessary

Diagnosis of infectious diseases of various types - both viral and bacterial - is aimed at identifying pathogens at an early stage, which makes it possible to prescribe timely and especially effective treatment. The most modern method for detecting infections is PCR, which stands for polymerase chain reaction. What is the essence of this method and what is its purpose?

The essence of the polymerase reaction

The structure of any virus and microorganism contains RNA or DNA molecules. It is characteristic that these compounds are unique for each, and therefore, by isolating nucleic acids in a blood test in adults or children, a diagnosis can be made with absolute accuracy.

Unfortunately, the concentration of DNA, both in blood samples and in other biological materials, is quite low, so it cannot be determined by ordinary diagnostic methods. In order to cope with this problem, the polymerase chain reaction was invented at one time.

So, the essence of this analysis lies in the specific processing of the blood sample, due to which the concentration of DNA molecules increases in it, and the establishment of their type in the future makes it possible to identify the type of pathogen, as well as to make the correct diagnosis.

How is a PCR blood test performed?

The PCR method is carried out only in laboratory conditions. To carry it out, special enzymes are used that increase the structure of the patient's RNA and DNA several times. In this case, such a number of them should be formed to make it possible to conduct a visual study. During the survey, a copy of such a site is carried out, which fits the required conditions in all respects. What is a PCR blood test for RNA is interesting to many.

The laboratory has the necessary database available, which indicates the exact structure of various infectious agents. Using the PCR method allows not only to establish the type of pathogen, but also to calculate its quantitative proportion.

PCR diagnostics also includes some innovations, among which the following stand out:

Connection of various fragments of DNA;

Introduction of mutation;

Establishing paternity, etc.

What diseases are detected by PCR?

Thanks to PCR, it is possible to identify almost all bacterial and viral pathologies. For research, not only blood can be used, but also other biological materials, such as smears from the urethra and from the uterine cervix, saliva, and semen. The analysis becomes quite informative when the causative agent of a certain disease enters the human blood. That is why a blood test for PCR is prescribed for the following pathologies:

Viral hepatitis types A, B, C, D and TT;

Infection of a herpetic nature (that is, viruses of the first, second and fourth types);

Cytomegalovirus;

Enteroviral infection;

HIV infection;

Rubella;

Listeriosis;

Shingles;

Infectious mononucleosis;

Toxoplasmosis.

If we take into account the implementation of PCR using other biomaterials, then the following should be added to the list of pathologies that can be detected using this method:

salmonellosis;

Diphtheria;

Gardnerellosis;

Mycoplasmosis;

Tuberculosis;

Trichomoniasis;

- papillomavirus infection (about a hundred different strains of the human papillomavirus).

Of particular relevance has now become a PCR blood test during pregnancy for TORCH infections, which include toxoplasmosis, cytomegalovirus, herpesvirus infection and rubella. This is due to the fact that the above diseases can cause abnormalities in the development of the fetus.

Advantages of PCR

What are the advantages of this method?

• One hundred percent accuracy of diagnosis: if there are at least several DNA fragments of the pathogen in the blood, they will be determined by the PCR reaction, which means that the correct diagnosis will be made. This is the main difference between this method and other diagnostic methods - a complete blood count, ELISA and others.
• Specificity. During a PCR blood test for borreliosis, for example, there is no such thing as a false negative or false positive result, which distinguishes it from an enzyme-linked immunosorbent assay, or ELISA.
• The analysis can be carried out in order to determine several pathogens at once based on a single biomaterial sample, making this method convenient for the patient, because he does not have to take the analysis several times.
• Rapidity. There is no need to isolate and grow the pathogen on special nutrient media, which is necessary during bacteriological examination. You can get the finished result on the day of the analysis.

• By means of a PCR blood test for hepatitis, for example, a hidden causative agent of the disease in the body is determined when the patient acts as a carrier of the infection (HIV or hepatitis).
• Affordable price. The cost of PCR analysis to determine one pathogen ranges from two hundred and fifty to five hundred rubles. A semi-quantitative examination for viruses costs a little more - about a thousand rubles.

Disadvantages of the method

PCR is a high-tech research method that places high demands on laboratory equipment. The room for analysis must necessarily have a biological filter, since there are always particles of saliva and skin in the air, which contain DNA molecules. Failure to comply with the technical requirements for working with biomaterials can lead to misdiagnosis.

Who should take a blood test for PCR?

Anyone can take the survey. The indication for it is the suspicion of sexually transmitted infections (HIV infection, bacterial vaginosis, chlamydia). If unprotected sexual contact accidentally occurred, only PCR will make it possible to make a correct diagnosis at an early stage, if a person has become infected with a particular disease.

Blood for the TORCH-complex is mandatory for pregnant women, as well as those who are just planning to conceive a child.

Although PCR is the maximum effective method diagnostics, but you do not need to go in cycles in it. It is necessary to examine the patient in the presence of any pathology comprehensively. If the polymerase chain reaction makes it possible to determine the pathogen, then thanks to a serological study, it is possible to assess the level of effectiveness of therapy, the reaction of the human body to the pathogen and medications. A PCR blood test for HIV should be ordered by a doctor.

Features of the procedure and preparation

Patients who are examined using the PCR technique receive the most reliable result. It must be said that in this case the probability of errors is almost completely eliminated. The results of this analysis are also prepared quite quickly, which makes it easier to determine the diagnosis and it becomes possible to prescribe the necessary medical procedures in a timely manner.

The reliability of the result obtained by the PCR method is determined by the correct delivery of biological material for examination. It should not be contaminated with anything, otherwise the result will not be objective.

• a ban on sexual intercourse a day before the procedure;
• a blood test to detect infections should be taken in the morning and only on an empty stomach;
• urine is also given in the morning in a sterile container.

One and a half or two days after the procedure, the PCR blood test will be decoded and the result is ready. There are even cases when you can get the result on the same day.

How to prepare material for analysis?

In order to conduct the study as successfully as possible, it is necessary to correctly take the material from the patient and conduct its competent preparation. It is a well-known fact that in a laboratory study a large number of errors (up to approximately seventy percent) occur during sample preparation.

Currently, in some laboratories, blood is taken using vacuum systems. On the one hand, they minimally injure the patient, on the other hand, they make it possible to take the material so that it does not come into contact with either the environment or the personnel. This avoids contamination of the biological material and maximizes the reliability of the analysis.

Deciphering the results

The result of a blood test for PCR can be positive or negative. If the blood test is negative, then this indicates the absence of infectious pathogens in the material handed over by the patient. A positive analysis confirms that there are infectious agents in the blood, which means that the most effective and high-quality treatment of the patient is required.

The result obtained can be positive even in the absence of any symptoms of the disease. This indicates either the beginning of the pathological process, or that the person is a carrier. If the latter is detected, no medical procedures are required. In this case, the patient is recommended to be constantly monitored by a doctor, which implies, for example, a periodic PCR blood test for herpes and other infections.

Most often they are found in the urethra, in scrapings made from the cervical canal, in saliva. However, it must be remembered that a sick person is able to infect perfectly healthy people, even if he is not bothered by this disease. It may become chronic. It must be said that with a positive result obtained using PCR, it is necessary to prescribe appropriate medical procedures.

Quantitative characterization of PCR

A PCR blood test for infections is also characterized quantitatively. Such a result can only be assessed by a specialist, since it is individual for various infections. It is the quantitative characteristic that allows the doctor to determine the degree of activity of such a pathological process, to determine the exact stage of development of a particular disease.

The study of the results obtained will help the specialist choose the appropriate drug, specify the required dosage.

Diagnostic accuracy

There are three most important characteristics of PCR, namely:

Sensitivity;

Specificity;

Accuracy.

Diagnosis of infections using PCR is characterized by a high probability of detecting infectious agents in the body. Analysis of blood and other fluids is highly specific. Thanks to him, you can easily determine a specific infectious process by passing, for example, a PCR blood test for hepatitis or HIV. Also, PCR diagnostics is highly sensitive. If there is a minimum number of infectious agents in the test material, the PCR method will always be positive.

In very rare cases, a false positive result can be obtained. In the absence of infection, it will, accordingly, be negative.

Identification of hidden diseases

If a person is suspected of having an STI, a blood test is prescribed to determine hidden infections. Any diseases of the genital area can only be determined by examining the patient.

The following diseases can have a latent nature of the course:

• ureaplasmosis;
• chlamydia;
• mycoplasmosis;
• herpes;
• gonorrhea;
• gardnerellosis.

These infections are quite common and very insidious. At the beginning of the disease, they do not have well-defined symptoms, so patients do not go to a specialist. The results of a timely PCR blood test for chlamydia, borreliosis and other infections will help the doctor prescribe an effective treatment.

STIs adversely affect the reproductive system. They can cause infertility or the appearance of defects in the fetus. That is why it is important to take a PCR test before planning a pregnancy.

Content

Those who are interested in new diagnostic methods should find out what the PCR method is. Modern technical capabilities in the field laboratory research provide an opportunity to detect many diseases in the initial stages. Polymerase chain reaction (PCR) is currently considered the most accurate and new method.

PCR analysis

PCR analysis - what is it? This method uses the principles of molecular biology. To study the material, special enzymes are used that repeatedly and quickly copy DNA, RNA fragments of pathogens. Exists different types PCR analysis depending on the material being studied (blood, urine, feces, etc.). After processing, laboratory staff compare the result with the database, identify the concentration, type of pathogen.

The PCR analysis is placed in a special amplifier (device) that heats and cools the test tubes with the biomaterial. Temperature changes are needed for fragment replication. The accuracy of the result will depend on the accuracy of the temperature regime. The polymerase chain reaction method helps to identify:

• Infectious mononucleosis;
• cytomegalovirus infection;
• viral hepatitis G, C, B, A;
• sexually transmitted infections / diseases (STIs / STDs): gardnerellosis, trichomoniasis, ureaplasmosis;
• herpetic infection;
• oncogenic viruses;
• listeriosis;
• helicobacter infection;
• tick-borne encephalitis, borreliosis;
• tuberculosis;
• candidiasis.

Blood

At the moment, due to the novelty of the technology, the PCR blood test still has a high price. For the preparation of biomaterial it is not necessary to comply with certain requirements. Even caused by physical activity, stress, change in diet, changes in the composition do not affect the result of the study. A PCR blood test can only spoil the intake of antibacterial agents, therefore, before taking it, it is necessary to pause between treatment and the test.

PCR blood test is the most common option for diagnosing chronic, acute infectious pathologies with a viral or atypical manifestation. Serological research methods have a certain difficulty in carrying out - the presence of a pathogen is determined by the presence of antibodies in the human body. The result could be false negative if the patient's condition did not give time for their development.

smear

In the field of gynecology, PCR smear analysis is used to study the presence of infectious microorganisms. Working with the material is carried out according to the same principle as with blood: a multiple increase in DNA fragments of the pathogen in order to easily identify it. It also helps to detect hidden infections in a woman. Various biological fluids can be taken for analysis: saliva, sputum, urine, blood. In gynecology, for the accuracy of the determination, a smear from the vaginal mucosa from the cervical canal is more often used.

There are certain indications for PCR. Often it needs to be done to identify an antibiotic-resistant type of pathogen. In women, the main indications for diagnosis by this method are:

• a pregnancy that is difficult;
• acute phase of STIs;
• if there is a suspicion of the transition of STIs to the chronic stage;
• search for causes of infertility.

Cala

To detect infection, a fecal PCR test may be prescribed by the doctor. In order to obtain the most reliable results after the test, it is necessary to adhere to the following rules before taking the biomaterial:

• stop taking laxatives for a few days: oils, suppositories;
• exclude medicines that give a specific color to the stool, for example, with iron content.

For sampling, use a sterile stick and container. Something to wipe them additionally, rinse is not necessary. When collecting material, be careful not to touch the inner walls of the container with your hand. Make sure that there are no impurities of urine in the feces, you can not use additional aids for bowel movements (enemas). You need to collect the material on the day of delivery, 1/3 of the container volume is enough. This diagnostic method has the following advantages:

Urine

If necessary, the doctor may take urine for testing. High accuracy opens up the possibility to work with any biological fluid from which it is possible to extract virus DNA. To pass a PCR urine test, you must adhere to the following restrictions before taking the material:

• at least 1 day before the procedure, stop sexual intercourse;
• 3 weeks before the delivery, any antibacterial treatment should be completed, because the medicines will blur the picture;
• you need to take the test on an empty stomach (liquid is also prohibited);
• you need to take the first morning portion of the material.

PCR test results

From the above, it is clear what PCR analysis is and the clear advantages of this research method are visible. Another plus of this diagnostic procedure is the ease of deciphering the results. Considering how much PCR analysis is done (the process itself takes about 5 hours, but the laboratory issues data in 1-2 days), this diagnostic method becomes the best option for determining many infections. Based on the results, your doctor may tell you that the test:

1. Negative - the studied material did not contain the desired pathogen.
2. Positive - RNA, DNA of the pathogen were found.

Sometimes quantitative determination of microorganisms is carried out. This is necessary for diseases that cause opportunistic pathogens. The peculiarity of these viruses is that they appear only in excess and it is extremely problematic to find them with conventional studies. This factor is important for the choice of therapeutic tactics in order to effectively treat viral infections, for example, hepatitis, HIV.

For 12 infections

To fully understand what PCR is for diagnosing infections and how effective it is, you need to know that it is capable of isolating up to 12 pathogens. The text is carried out only in laboratory conditions. For research, special enzymes are used, which increase many times the amount of RNA, DNA fragments of the virus. PCR analysis for 12 infections can reveal:

• mycobacterium tuberculosis;
• cytomegalovirus;
• hepatitis C, G, B, A;
• herpes 1, 2 types;
• Epstein-Barr virus (infectious mononucleosis);
• infections that are sexually transmitted by, for example, chlamydia;
• listeriosis;
• candida infection;
• helicobacter pylori;
• borreliosis, tick-borne encephalitis.

For hepatitis C

This diagnostic method helps to determine the presence of the virus in the blood. This gives doctors the opportunity to talk about its presence or absence. There are two types of PCR analysis for hepatitis C: qualitative and quantitative. The first option indicates only its presence and can be worded "detected" / "not detected". This type of test has a sensitivity of 10-500 IU/ml. This suggests that with a low content of the pathogen in the body, the analysis will be “not detected”.

Quantitative analysis is more accurate and will show the concentration of infection in the blood. This indicator is designated as "viral load", measured in the amount of viral RNA per specific volume of blood. Decryption in different laboratories may vary. In addition to measuring in IU / ml, "copy" units are used. You can recalculate copies per IU using the formula: 1 IU = 4 copies. If in the transcript the value of the presence of the virus exceeds 800,000 IU / ml (or 800 * 103), this indicates a high content of the pathogen.

For tuberculosis

The test should be done in the morning. This is important in order to prevent all the sputum that formed during the night from leaving the stomach. PCR analysis for tuberculosis is as important as ELISA, Mantoux, tomography. The test helps to identify the presence of mycobacteria, the state of urine, total immunoglobulin, ESR, and determine the state of the lungs at the moment. For the accuracy of obtaining results in the analysis of PCR, it is necessary to carry out it in compliance with the following rules:

1. Sowing is carried out 3 times, but complete aspiration of the contents of the stomach should be carried out only in a hospital.
2. Detects mycobacteria by culture of existing masses in the stomach in less than 50% of diagnoses. Even when optimal conditions are obtained, ultrasound is recommended instead.
3. Even with a negative result, the likelihood of developing tuberculosis with a change in ESR, immunoglobulin or other indicators cannot be completely excluded.
4. PCR culture is less susceptible to pathological conditions if it is obtained as part of a bronchoscopic examination, which excludes suspicion of TB in a child.

For HIV

For many people, this diagnosis is considered a death sentence. For this reason, after frequent sexual intercourse, a person becomes more attentive to the signals that his body gives (and sometimes comes up with them). The most reliable option to get confirmation or refutation of this disease is a PCR test for HIV. The test can be used to identify the following possible health problems:

1. Denial/confirmation of the presence of HIV during the period of the seronegative horse.
2. Determination of the genotype of HIV-1, HIV-2.
3. Clarification of the description of the pathological process with a doubtful result of the immunoblot.
4. Infection after blood transfusion.
5. Determining HIV status in children born to carrier mothers.
6. Helps to establish monitoring of the viral load of the body.

For HPV

The papilloma virus can be detected in any person, for a long time it can be in a latent state. Development provokes a weakening of the immune system, stress or emotional outbursts. PCR analysis for HPV helps to determine the concentration of the virus in the blood. For this reason, it is recommended to carry out a quantitative determination rather than a qualitative one. These data will help predict the likelihood of developing a malignant nature of the infection.

The technique for diagnosing the presence of HPV is based on the main property of PCR to isolate virus DNA from the material. Due to the high sensitivity of the test, even a small amount of bacteria will be detected. Quantitative research gives doctors the opportunity to determine the degree of danger of the disease, to make a prognosis for the future. This diagnosis is mandatory for all men and women who have found themselves with warts. Quantitative PCR analysis will help determine what caused the development of HPV: a temporary decrease in immunity or a chronic disease.

For herpes

This type of diagnostics in microbiology helps to carry out PCR analysis for herpes with high accuracy. Copying of DNA fragments of the virus will occur only if the desired gene is present in the material. In this case, the test based on the results of the conduct may indicate the presence or absence of the pathogen. It will be possible to detect it even at low concentration in the blood.

Another plus of the PCR analysis is that it can detect a herpes virus infection immediately after infection, before the onset of clinical symptoms. It is possible to determine the type of herpes (1 or 2), no specific preparation is required to pass the analysis, but doctors recommend that you refuse before taking blood:

• fried;
• acute;
• alcohol;
• fatty.

During pregnancy

When carrying a child, it is very important to conduct this study in order to take into account the condition of the woman. PCR analysis during pregnancy is included in the list of the most effective methods for determining the presence of a variety of diseases. It is necessary to conduct a test not only to identify pathologies, but also to determine the likelihood of infection of the child in utero. Only thanks to PCR diagnostics, it became possible to identify the degree of progression, the development of many infections inside the mother's womb.

Delivery of PCR analyzes

If you are wondering how the PCR analysis is taken, then each individual case should be considered, taking into account the type of biomaterial. Scraping, smear or blood sampling has its own characteristics, for example.

Polymerase chain reaction (PCR) is a high-precision method in the field of diagnosing hereditary pathologies, infections, viral diseases at any stage (acute or chronic), as well as - at an early stage - before obvious manifestations of the disease by identifying pathogens based on their DNA, RNA , which are genetic material, in samples that are obtained from the patient. And today we will talk about the essence, diagnostic stages and principles of polymerase chain reaction (PCR) methods, as well as its cost.

What is polymerase chain reaction

The basis of the analysis is amplification (doubling) - the creation of many copies from a short section of DNA (deoxyribonucleic acid), which represents the human genetic complex. The study requires a very small amount of physiological substances (sputum, feces, scrapings of the epithelium, prostate juice, blood, semen, amniotic fluid, mucus, placental tissue, urine, saliva, pleural fluid, cerebrospinal fluid). In this case, for example, even a single harmful microbe can be detected in the urogenital tract of a patient.

The PCR technique (polymerase chain reaction) was developed by the American scientist K. Mullis, who received the Nobel Prize in 1993.

Actively used:

• in the early diagnosis of infections, genetic,;
• in forensic medical examination in the presence of an extremely small amount of DNA for research;
• in veterinary medicine, pharmaceuticals, biology, molecular genetics;
• for identification of a person by DNA, confirmation of paternity;
• in paleontology, anthropology, ecology (when tracking the quality of products, environmental factors).

This video will tell you what a polymerase chain reaction is:

To whom is it assigned

Polymerase chain reaction in the diagnosis of infectious diseases is one of the most reliable methods of high accuracy and reliability. For example, the reliability of the PCR analysis for chlamydia and many other pathogens approaches 100% (absolute). Most often, the polymerase chain reaction procedure is prescribed to patients who, when diagnosing, have difficulty identifying a specific pathogen.

Laboratory PCR test is used:

• to detect pathogens that cause infection of the urinary and genital organs, which are difficult to identify using crops or immunological methods;
• for re-diagnosis of HIV at the initial stage in the case of a positive, but questionable result of the initial analysis (for example, in newborns from parents infected with AIDS);
• to establish an oncological disease at an early stage (study of oncogene mutations) and individual correction of the treatment regimen for a particular patient;
• for the purpose of early detection and potential treatment of hereditary pathologies.

So, future parents are tested to find out if they are carriers of a genetic pathology; in children, PCR determines the likelihood of exposure to a hereditary disease.

• to detect fetal abnormalities early term gestation (individual cells of a growing embryo are examined for possible mutations);
• in patients before organ transplantation - for "tissue typing" (determining tissue compatibility);
• to detect dangerous pathogenic organisms in donated blood;
• in newborn babies - to detect latent infections;
• to evaluate the results of antiviral and antimicrobial treatment.

Why go through this procedure?

Since PCR is a highly effective diagnostic method that gives an almost 100% result, the procedure is used:

• to confirm or exclude the final diagnosis;
• rapid assessment of the effectiveness of the therapy.

In many cases, PCR is the only possible test for detecting a developing disease if other bacteriological, immunological and virological diagnostic methods are useless.

• Viruses are detected by PCR immediately after infection and before signs of illness appear. Early detection of the virus allows prompt treatment.
• The so-called “viral load” (or the number of viruses in the body) is also determined by quantitative DNA analysis.
• Specific pathogens (such as Koch's tubercle bacillus) are difficult and take too long to culture. PCR analysis allows you to quickly identify the minimum number of pathogens (live and dead) in samples that are convenient for research.

Detailed pathogen DNA analysis is used:

• to determine its sensitivity to specific types of antibiotics, which allows you to immediately begin treatment;
• to control the spread of epidemics among domestic, wild animals;
• to identify and monitor new contagious microbial species and pathogen subtypes that have fueled previous epidemics.

Types of diagnostics

Standard method

Analysis of the polymerase chain reaction is carried out on the basis of multiple amplification (doubling) of a specific DNA and RNA fragment using special primer enzymes. As a result of the chain of copying, an amount of material sufficient for research is obtained.

During the procedure, only the desired fragment is copied (corresponding to the specified specific conditions) even if it is actually present in the sample.

This detailed video with useful diagrams tells how PCR works:

Other Methods

• Real-time PCR. In this type of study, the process of identifying a given DNA fragment starts after each cycle, and not after the entire chain of 30-40 cycles has been completed. This type of study allows you to obtain information about the amount of a pathogen (virus or microbe) in the body, that is, to carry out a quantitative analysis.
• RT-PCR (reverse transcription mode). This assay is used to find single-stranded RNA to detect viruses whose genetic base is RNA (for example, hepatitis C virus, immunodeficiency virus). In such a study, a special enzyme is used - reverse transcriptase and a certain primer, and single-stranded DNA is built on the basis of RNA. Then a second DNA strand is restored from this strand and the standard procedure is performed.

Indications for holding

The PCR procedure is used in the clinic of infectious diseases, neonatology, obstetrics, pediatrics, urology, gynecology, venereology, neurology, nephrology, ophthalmology.

Indications for the purpose of the analysis:

• clarification of the risk of developing genetic abnormalities in a child with the likelihood of hereditary pathologies;
• diagnosing both parents when planning a pregnancy or a serious condition of the mother during an ongoing pregnancy;
• difficulties with conception, identification of the causes of infertility;
• suspicion of sexual infections in the acute stage and with symptoms of their transition to chronic;
• detection of causes of inflammatory processes of unclear origin;
• unprotected casual and constant sexual contacts;
• determination of the sensitivity of a pathogenic microorganism to specific antibiotics;
• patients with suspected latent infection to detect pathogens before the development of overt symptoms (preclinical diagnosis);
• patients to confirm recovery after illness (retrospective diagnosis);

Diagnostics is also used if it is necessary to accurately identify the following pathogens:

• hepatitis viruses (A B C G), human immunodeficiency, cytomegalovirus;
• vibrio cholera;
• herpes simplex virus, herpetiform species;
• retro - adeno - and rhinoviruses;
• rubella viruses, Epstein-Barr, varicella (Zoster - virus);
• parvo and picornaviruses;
• bacterium Helicobacter pylori;
• legionella, pathogenic types of Escherichia coli;
• staphylococcus aureus;
• pathogen;
• Clostridia, diphtheria and Haemophilus influenzae;

It is also used to determine infections:

• Infectious mononucleosis;
• borreliosis, listeriosis, tick-borne encephalitis;
• candidiasis caused by Candida fungi;
• sexual infections - trichomoniasis, ureaplasmosis, pale treponema, gardnerellosis, gonorrhea, mycoplasmosis, chlamydia;
• tuberculosis.

Contraindications for holding

Since the procedure is not carried out with the patient, without any effect on the body, but with biological material taken for research, there are no contraindications for PCR due to the absence of potential danger.

However, biomaterial sampling from the cervical canal of the uterus is not carried out after the colposcopy procedure. The delivery of smears, scrapings for analysis is allowed only 4 to 6 days after the end of menstruation and the complete cessation of discharge.

Is the method safe

No negative impact on the patient in an isolated study of his biomaterial in the laboratory is possible.

Preparation for the procedure (delivery of biological substances for analysis)

As a sample for PCR analysis, in which the DNA of a foreign pathogen is detected, any biological fluid, tissue, body secretions are used. The sampling of the test substance is carried out in the form of taking blood from a vein, scraping from the larynx, nasal cavity, urethra, pleural cavity, cervix.

Before the diagnostic procedure, the doctor explains to the patient what material will be taken:

1. When examining for sexual infections, secretions from the genital organs, urine, and a smear from the urethra are taken.
2. When analyzing for herpetic infections, cytomegalovirus, mononucleosis - they take urine, a throat swab for analysis, for hepatitis, toxoplasmosis - blood from a vein.
3. In order to diagnose various types, cerebrospinal fluid is taken.
4. In pulmonology, samples for analysis are sputum and pleural fluid.
5. When conducting a study of possible intrauterine infections during gestation, amniotic fluid and placental cells are used for analysis.

The reliability and accuracy of the analysis depends on the sterility of the conditions when taking the material. Since the PCR test is highly sensitive, any contamination of the test substance can distort the result.

Competent preparation for the delivery of biomaterial does not present any difficulties for patients. There are certain recommendations:

• when analyzing for sexual infections:
  • exclude intimate contacts 72 hours before the delivery of the material;
  • stop using any vaginal products for 3 days;
  • since the evening of the previous day, do not carry out hygiene of the area under study;
  • exclude urination for 3-4 hours when taking a sample from the urethra;
• stop taking antibiotics a month before testing for infections;
• donate blood in the morning before eating and drinking;
• the collection of the first morning portion of urine is carried out in a sterile container after a thorough intimate toilet.

Read more about how diagnostics are carried out using the polymerase chain reaction method.

How is the procedure

When performing a PCR study over and over again in the reactor (amplifier or thermal cycler), certain cycles are repeated:

1. The first step is denaturation. Saliva, blood, biopsy, gynecological samples, sputum, in which the presence of DNA (or RNA) of the pathogen is suspected, is placed in an amplifier, where the material is heated and the DNA is split into two separate chains.
2. The second step is annealing or slight cooling of the material. and adding primers to it that can recognize the desired sections in the DNA molecule and bind to them.
3. The third step is elongation- occurs after the addition of 2 primers to each of the DNA strands. During the process, the DNA fragment of the pathogen is completed, and its copy is formed.

These cycles are repeated like a "chain reaction", each time leading to a doubling of copies of a specific DNA fragment (for example, a segment where a certain virus is programmed). In a few hours, many copies of the DNA fragment are formed, and their presence in the sample is detected. After that, the results are analyzed and compared with the database of various types of pathogens in order to determine the type of infection.

Read about the interpretation of the results and the conclusion based on the PCR reaction below.

Deciphering the results

The final result of the study is issued 1-2 days after the delivery of biological material. Often - already in the first day after the analysis.

Qualitative Analysis

• Negative the result means that no traces of infectious agents were found in the substance submitted for research.
• Positive a result means the detection of pathogenic viruses or bacteria in a biological sample with a very high degree of accuracy at the time of submission.

If the result is positive, but there are no signs of activation of the infection, this state of the body is called asymptomatic “healthy carriage”. Most often observed when taking biomaterial from a certain place (cervical canal, urethra, oral cavity) in viral diseases. Treatment in this case is not required, but constant medical supervision is necessary, since there is a possibility:

• spread of the virus from carriers and infection of healthy people;
• activation of the process and the transition of the disease to a chronic form.

However, if the blood test is positive, this indicates that the infection has affected the body, and this is no longer a carrier state, but a pathology that requires immediate specific therapy.

Quantitative Analysis

The quantitative result is determined by the specialist specifically for a particular type of infection. On its basis, it is possible to assess the degree of development, the stage of the disease, which makes it possible to promptly prescribe the correct treatment.

average cost

The prices for conducting a polymerase chain reaction are determined by: the type of study, the complexity of identifying the pathogen, the difficulty of collecting biological material, the type of analysis (qualitative or quantitative), the price level in the laboratory.

On the other hand, in the study of PCR, several pathogens can be detected at once when taking one type of material for analysis. This saves on other laboratory tests.

Approximately, the cost of PCR analysis in rubles:

• gonococcus, gardnerella, trichomonas vaginalis - from 180
• chlamydia trachomatis - from 190
• papillomavirus - from 380 to 500
• biocenosis of the urogenital tract in women (quantitative and qualitative assessment of microflora) - from 800.

Even more useful information regarding the PCR study, see the video below:

Polymerase chain reaction (PCR) is a high-precision method of molecular genetic diagnostics, which makes it possible to detect various infectious and hereditary diseases in humans, both in the acute and chronic stages, and long before the disease can manifest itself.

The polymerase chain reaction (PCR) was developed in 1983 by Cary Mullis (USA), for which he was awarded the Nobel Prize in Chemistry in 1993.

PCR analysis has become a kind of “gold standard” for most infections. Most specialists face it almost daily and cannot imagine making a final diagnosis without it. PCR often becomes the only reaction to detect the active stages of the disease at those moments when other bacteriological, virological, immunological diagnostic methods do not work.

Advantages of PCR diagnostics in modern medicine:

Direct detection of the presence of a pathogen (namely, a specific region of DNA or RNA of the pathogen) in the test sample.
High specificity makes it possible to determine a unique section of DNA or RNA characteristic of a particular pathogen, which eliminates the possibility of false reactions.
The high sensitivity of the PCR method makes it possible to detect even single cells of pathogens (viruses, bacteria). The sensitivity of PCR analysis is 10-1000 cells in the test sample (for example, the sensitivity of immunological and microscopic tests is only 103-105 cells).
Development of a universal PCR technique for the detection of various pathogens. The object for research by PCR is the genetic material (DNA, RNA) of the pathogen. The technique allows to detect several pathogens from one biological sample.
Relatively fast analysis results. A complete study is carried out in 4-4.5 hours, less often - a little longer.
The ability to detect pathogens before the onset of symptoms of the disease (preclinical diagnosis) and after the past disease (retrospective diagnosis). An example of preclinical diagnosis would be an examination during the incubation period (from the moment of infection to the onset of patient complaints), as well as a latent infection (when there are no symptoms at all, but there are only laboratory data - PCR, for example). One of the important points of PCR diagnostics is PCR in archival material or biological remains, which is important for identifying a person or paternity.

Currently, PCR diagnostics is undergoing significant development. The method itself is being improved, new types of PCR appear again and again, new test systems for this reaction enter the medical market. Due to this, the cost of PCR studies is becoming more affordable for a wide range of patients every year.

What is the basis of the PCR method

The basis of the polymerase chain reaction is the repeated doubling (amplification) of a certain section of DNA or RNA using enzymes in the laboratory. As a result, the amount of DNA or RNA sufficient for visual analysis is formed. During the study, only the area that fits the specified conditions is copied, and only in the situation of its presence in the test sample.

For example, a material for research, in which the presence of fragments of DNA or RNA of the pathogen (saliva, blood, urine, secretions from the genital organs) is expected, is placed in a special reactor (amplifier). Further, specific enzymes are added to it, which bind to the DNA or RNA of the pathogen, and a copy of it is synthesized. This copying takes place in several stages, like a "chain reaction", and ultimately from one copy genetic material hundreds and thousands of copies can be formed. Then comes the analysis and comparison of the result with the existing database on the structure of various pathogens. Through PCR, you can not only identify the type of pathogen, but also give a quantitative result of the analysis, that is, how many pathogens are in the human body.

The PCR method is currently expanding the range of possibilities for ongoing research: the introduction of mutations, splicing of DNA fragments, and is widely used in medicine, for example, to establish paternity, the emergence of new genes, and so on.

What infections can be detected using PCR diagnostics

1) HIV infection (human immunodeficiency virus HIV-1 can be detected)
2) Viral hepatitis A, B, C, G (RNA-HAV, DNA-HBV, RNA-HCV, RNA-HGV)
3) Infectious mononucleosis (DNA of the Epstein-Barr virus - EBV)
4) Cytomegalovirus infection (DNA-CMV)
5) Herpetic infection (DNA - herpes simplex virus HSV types 1 and 2)
6) STIs (sexually transmitted infections) - ureaplasmosis, gardnerellosis, chlamydia, mycoplasmosis, trichomoniasis,
7) Tuberculosis (mycobacterium tuberculosis)
8) Oncogenic viruses - papillomavirus infection (human papillomavirus (including its oncogenic species 16, 18, 31, 33, 45, 51, 52, 56, 58, and 59)
9) Borreliosis, tick-borne encephalitis
10) Listeriosis
11) Candidiasis (fungi of the genus Candida)
12) Helicobacter pylori infection
and others

Considering the spectrum of pathogens, PCR diagnostics is actively used in gynecological, urological, infectious disease practice, pulmonology, phthisiology, gastroenterology, hematology, oncology, and others.

Material for research and rules for its collection

The material for PCR research, in which foreign DNA of a bacterium or DNA or RNA of a virus can be detected, can be various biological media and human fluids: mucus, urine, blood, sputum, scraping of epithelial cells, placental tissues, blood, prostate juice, amniotic fluid, pleural fluid.

When screening for sexually transmitted infections (STIs), men and women take secretions from the genital organs, a smear or scraping from the cervix, a swab or scraping from the urethra (urethra), urine.

When examining for infections (herpetic infections, CMVI, mononucleosis, toxoplasmosis, hepatitis B, C, HIV infection), blood is taken for PCR.

For the diagnosis of infectious mononucleosis, CMVI, herpetic infection, a swab is taken from the throat, for examination for CMVI - urine. Often, cerebrospinal fluid is taken to examine for damage to the nervous system in a number of studies.

In pulmonology, the material is sputum, pleural fluid.

When examining intrauterine infections - amniotic fluid, placental tissue.

Preparation for the delivery of material and PCR diagnostics

Almost all patients who undergo PCR diagnostics have the right to count on a reliable, accurate and fast result, which depends to a large extent on the capabilities of the laboratory and the professionalism of the laboratory assistant. At the same time, many do not think that this very reliability largely depends on ourselves, namely on the recommendations of the attending doctor, lifestyle and the correctness of the material sampling. When sampling material, conditions are required that exclude contamination (contamination) of the material and, accordingly, cast doubt on the objectivity of the analysis.

Proper preparation for the delivery of the material is not particularly difficult. There are following recommendations of doctors for patients:

1) not to live sexually a day before the delivery of the material;
2) blood for research is given in the morning on an empty stomach (do not eat, do not drink);
3) when passing urine, the first morning portion is collected in a clean sterile container.

Deadlines for PCR analysis

The final result is ready in 1.5-2 days after the delivery of the material. In some cases, the result is ready on the first day.

Interpretation of PCR results

Negative the PCR result indicates that no traces of infectious agents were found in the test material at the time of its delivery. Most of the cases show the absence of the infection that was tried to be found in the test sample.

Positive the result of PCR indicates the detection of traces of infection in the biological sample under study. With great accuracy, a positive result indicates the presence of infection at a given time.

There are situations when PCR is positive, but it is impossible to talk about an active infection - this is the so-called "healthy carriage" without clinical symptoms of the disease, which does not require treatment, but requires dynamic observation by a doctor. It is observed more often in a number of viral infections (HPV, CMVI, EBV infection, herpes infection, and others) in materials such as saliva, scraping of the cervical canal, urethra, that is, from a local focus. However, we must not forget that the transmission of infection from carriers to healthy people is possible, as is the transition to the chronic form of the disease with the activation of the process. If PCR is positive in the blood, then this is no longer a carrier state and requires specific treatment.

The quantitative result of PCR is evaluated only by a doctor individually for a particular infection separately and does not have general gradations. Based on the quantitative PCR result, the doctor can determine the degree of infection activity and set the stage of the disease, which will certainly affect the course and doses of prescribed drugs.

One of the last exciting questions: how accurate is PCR diagnostics?

There are 3 definitions for PCR analysis:

1. Accuracy (with a high degree of probability, detection or absence of infection is possible).
2. Specificity (accuracy in detecting a specific infection).
3. Sensitivity (even with a low content of the genetic material of pathogens in the test sample, the infection will be detected).

Polymerase chain reaction practically does not produce false positive results (that is, there are no positive samples where there is no infection). False-negative results are rare (more often this is due to the absence of an active infection in a person at the moment). For example, latent infection, chronic infection out of activity.

Infectious disease specialist Bykova N.I.

Video on why and how to take a PCR test for infections

The essence of the PCR diagnostic method

The polymerase chain reaction (PCR) method is based on the principles of molecular biology and belongs to the field of genetic research.

Any living organism contains in its structure molecules of nucleic acids - DNA and RNA. This is a kind of genetic passport, which helps to determine which species this or that “bearer” belongs to. However, in order to scan this "passport", until recently, a certain minimum amount of biological material was required. If the DNA concentration was lower than necessary, diagnostic analysis was not possible.

When diagnosing by PCR, a sample of biological material is treated with special enzymes (polymerases), which allow you to start the process of multiple copying of existing DNA (RNA). Using a chain reaction cascade, according to the principle of geometric progression, in just a few hours, several tens of trillions of copies can be obtained from one nucleic acid molecule. This volume is more than enough for any comparative studies.

For analysis, an amplifier is used, in which, under strict temperature conditions, the process of multiple DNA replication takes place. Usually 20-30 replication cycles are sufficient. Each of them includes 3 consecutive stages:

• denaturation - heating the DNA matrix to 96°C with the destruction of hydrogen bonds between adjacent chains;
• annealing - lowering the temperature by 4°C to create a replication fork;
• elongation - the launch of DNA polymerases for the synthesis of new nucleotide chains based on the mother.

Each three-stage cycle lasts an average of 15-20 minutes.

Benefits of PCR diagnostics

PCR analysis is high-tech and requires professionalism from laboratory staff, but for modern medicine it has become a source of unprecedented opportunities in the field of accurate diagnostics.

Advantages of PCR:

• universality (any biological material can be examined - from blood cells, saliva and hair to suspicious spots at the crime scene);
• high threshold of sensitivity (the method is able to give a result in the presence of single cells or individual DNA molecules in the sample);
• multitasking - in one approach, several different types of information carriers can be detected at once (bacteriological methods are not capable of this, since they require different nutrient media for each type of microorganism);
• the ability to conduct accurate quantitative analysis;
• processing speed (unlike other types of genetic studies, PCR diagnostics takes only 5-7 hours);
• accuracy of the result (if the technology is observed, the error is practically excluded);
• relatively low cost (PCR analysis does not go beyond the average price for standard tests).

All these advantages make it possible to use the polymerase chain reaction for regular monitoring of the treatment process.

The developer of the PCR diagnostic method received the Nobel Prize for his “brainchild” for a reason. The polymerase chain reaction method allows:

• determine the strain of an infectious agent with a minimum content in the biomaterial (up to single viral structures);
• calculate the exact concentration of the pathogen in the whole body (to determine the optimal dose of drugs);
• assess the degree of pathological effects on the patient and identify strains with high pharmacological resistance;
• establish successive stages of infection and make a further prognosis.

It is interesting! The possibilities of PCR analysis are much wider than the quantitative and qualitative assessment of the infectious background in the human body. In addition to detecting infections, it is used to establish kinship, determine personality, identify genetic pathologies, and compare biomaterial in forensic science.

What infections can be detected by PCR diagnostics

PCR analysis is able to calculate with high accuracy any infectious carrier included in the modern medical catalog of diseases:

• causative agents of hepatitis of all types (PCR allows you to identify the source of infection at the stage of the incubation period and start treatment long before the onset of symptoms of the disease);
• pathogens of HIV and STDs (ureaplasmas, mycoplasmas, chlamydia, trichomonas);
• a group of TORCH infections (relevant when examining pregnant women for early detection of fetal pathologies);
• tuberculosis (latent form of the disease);
• candidiasis (latent form);
• enterovirus infection;
• mononucleosis;
• listeriosis;
• salmonellosis (definition of a specific strain);
• papillomavirus;
• gardnerellosis;
• tick-borne encephalitis virus.

Particularly popular is the analysis for intracellular infections (for example, chlamydia), the determination of which in the usual way is difficult even with a high concentration of these microorganisms in the patient's tissues.

Given the multitasking of the method, it is possible to make a simultaneous PCR analysis for 12 basic infections. An integrated approach is a convenient choice for routine body screening for sexually transmitted infections with minimal risk of misdiagnosis.

On a note! With the help of PCR diagnostics, a forecast is made for the so-called "sleeping" forms of infections that are in the body without manifesting themselves as symptoms of the disease (especially important in the treatment of gynecological and urological diseases, tuberculosis, tick-borne encephalitis, papillomavirus).

What biological materials are being studied

There are no set rules or boundaries. The versatility of the method allows the use of any biological material for analysis:

• vaginal swab, scraping from the urethra and cervical canal (for the diagnosis of STDs);
• urine (tuberculosis, some STDs, cytomegalovirus);
• blood (HIV, hepatitis, TORCH infections);
• throat swab (mononucleosis, cytomegalovirus);
• liquor (neuroinfection)
• amniotic fluid and placental tissues (analysis for TORCH infection to prevent pathologies of fetal development);
• pleural fluid (lung infections).

For other types of PCR diagnostics (establishment of kinship, comparison of biomaterial), saliva, hair, nails, epithelial cells and other sources of genetic information are used.

On a note! The method of PCR diagnostics reveals pathogens not only in the composition of living tissues, but also in samples of soil, water, plant substrates; evaluate the pathogenic activity of microorganisms both in the human body and in its environment (the presence of an established source of the disease will allow taking appropriate measures to prevent it in the future).

How to prepare for the analysis

Patients of our clinic do not need to wonder where to take a PCR test. We provide all conditions for sterile sampling of material and sending it to the laboratory.

Special training is not required, but it is advisable to follow a list of general recommendations. Give up alcohol for a few days, limit smoking, if possible, exclude medications, try to avoid stressful situations and heavy physical exertion.

The rest of the preparation for passing the analysis depends on the type of biomaterial:

• before taking a smear or scraping for urogenital infections, refrain from sexual intercourse for 2-3 days (women should make sure that the day of the test does not fall on the days of menstruation);
• before taking a blood test for PCR, refrain from eating in the morning (the test is taken on an empty stomach) and drink a glass of clean non-carbonated water;
• before passing urine, refrain from foods that affect the acidity of urine (fruits, meat, legumes, greens).

Important! The most important requirement in PCR diagnostics of infections is the purity of the biomaterial. Therefore, try to make every effort to exclude contamination of tissues with foreign DNA (take care of the sterility of the shipping container, personal hygiene, clean clothes).

Deciphering the PCR analysis

The results of a qualitative PCR analysis for infections are given in the form of a table, where each infectious agent has a corresponding mark:

• negative result (the causative agent of this species is absent);
• positive result (causative agent detected).

The absence of symptoms of the disease may not correspond to the real picture, so for someone the results of the analysis will be unexpected. You should not be upset: identifying an infectious agent in the early stages is the key to a successful and quick cure.

When conducting a quantitative PCR analysis, it is possible to assess the degree of viral load (find out the number of copies of the virus per unit volume). Thanks to this type of study, it is possible to determine the intensity of the course of the infectious process, as well as to evaluate the effectiveness of treatment.

PCR analysis: price and terms

The average diagnostic time is 5-10 hours. The results in the form of a table are issued the very next business day after the sampling of the biomaterial.

When choosing a PCR analysis, the price does not matter. On average, the amount of costs does not go beyond the scope of conventional biochemical tests and, unlike the bulk of genetic studies, is available to all patients.