PCR analysis: what is it? How to take the PCR test correctly

Not so long ago, a reliable, highly sensitive and rapid method for diagnosing various human infectious diseases was developed. This method is called "PCR analysis". What is it, what will its essence, what microorganisms it can reveal and how to properly hand it over, we will tell in our article.

History of the discovery

Invented the method of polymerase chain reaction (PCR) American scientist Cary Myullis in 1983. Initially patented method of diagnosis by the company "Cetus Corporation", in which his creator worked. But in 1992, all rights and patents were sold to the company "Hoffman-La Roche". After that, it appeared that parallel similar studies were conducted and were recorded by other American biologists, such as Alice Chen, David Edgar, John Treel. In 1980, Soviet scientists A. Slyusarenko, A. Kaledin and S. Gorodetsky dealt with this problem . Therefore, it was impossible to determine the sole rightholder. Many outstanding biochemists have contributed to the development of the polymerase chain reaction technique and patented their innovations. At the moment, PCR analysis is carried out everywhere in specially equipped laboratories.

The essence of the PCR diagnostic method

PCR analysis: what is it and how does it work? The essence of the method is to increase in a specific microbial medium by means of a special enzyme of DNA polymerase under artificial conditions. To do this, multiply the existing DNA-material. Thus, in the presence of a pathogenic microorganism in the sample, its amount will be increased through biochemical laboratory manipulations, and the bacterium can not be detected in a microscope.

How is the material research conducted?

The analysis requires:

• DNA-matrix;
• Primers connecting the ends of a fragment of material;
• A thermally stable DNA polymerase enzyme;
• Chemical substances that ensure the proper functioning of enzymes;
• A buffer solution necessary to create appropriate conditions for the growth and development of DNA material.

To carry out PCR, 25-30 repetitions are performed, consisting of three stages: denaturation, annealing and elongation.

To analyze the polymerase chain reaction, a special device is used - an amplifier. Modern equipment allows you to set the necessary program for heating and cooling the tubes to eliminate errors during the diagnosis.

Where is the diagnosis used?

The method of polymerase chain reaction is used in various fields of medicine:

• Forensic scientists use it to identify genetic material, for example hair, saliva or blood;
• Blood analysis PCR helps with genotyping, for example, to detect an individual genetically engineered reaction to a specific drug;
• With the help of such a method establish the existence of family ties between people;
• The most popular PCR method has become in medical diagnostics for the definition of various infectious diseases.

What infections reveal PCR?

So, medicine has long and successfully used the analysis of PCR. What is it, we already learned. And what pathogens can be detected with it? The following infectious diseases are diagnosed by PCR:

• Hepatitis A, B, C;
• Ureaplasmosis;
• candidiasis;
• Chlamydia;
• Mycoplasmosis;
• Gardnerellez;
• Infectious mononucleosis;
• Trichomoniasis;
• Papillomavirus infection;
• tuberculosis;
• Herpes infection of the 1 st and 2 nd types;
• Helicobacteriosis;
• Cytomegalovirus;
• diphtheria;
• Salmonellosis;
• HIV infection.

Also, PCR methods are used in the diagnosis of cancer.

Advantages

Diagnosis PCR has several advantages:

1. High sensitivity. Even with only a few DNA molecules of the microorganism, the PCR analysis determines the presence of infection. The method will help in chronic and latent diseases. Often in such cases, the microorganism is uncultivated in other ways.
2. For the study, any material, such as saliva, blood, sex, hair, epithelial cells, is suitable. The most common is the analysis of blood and urogenital smear on PCR.

3. It is not necessary to cultivate crops for a long time. Automated diagnostic process allows you to get the results of the study after 4-5 hours.
4. The method is practically absolutely reliable. Only single cases of a false negative result were recorded.
5. The ability to identify several types of pathogens from a single sample of material. This not only speeds up the process of diagnosis of the disease, but also significantly reduces material costs. Often the doctor prescribes a comprehensive PCR analysis. The price of the examination, consisting of the definition of six pathogens, is about 1500 rubles.

Recommendations for preparing for analysis

For the results to be reliable in the PCR study, the analysis should be performed following the recommendations for the preliminary preparation for diagnosis:

1. Before giving saliva, you should refrain from taking food and medication 4 hours before taking the material. Immediately before the procedure, rinse your mouth with boiled water.
2. The above rules should be followed when taking a sample from the inner surface of the cheek. After rinsing, it is recommended that a light skin massage be performed to isolate the secretion of the gland.
3. Urine is usually harvested at home. To do this, you need to conduct a thorough toilet of the genitals. It is necessary to collect 50-60 ml of urine in a sterile plastic container. To ensure the purity of the material, it is recommended that women insert a tampon in the vagina, and men maximally pull the skin fold. You can not take the material during menstrual flow.
4. For sperm delivery, you need to refrain from sexual intercourse for 3 days before taking the material. Also, doctors advise to refrain from visiting the sauna and taking a hot bath, drinking alcohol and spicy food. 3 hours before the test, you need to refrain from urinating.
5. For the delivery of a urogenital smear, for example, if an analysis is carried out on chlamydia PCR, both women and men are recommended to have sexual rest for 3 days. For 2 weeks before the test, antibacterial drugs should not be taken. For a week you need to stop using intimate gels, ointments, vaginal suppositories, douching. 3 hours before the test you need to refrain from urinating. During menstruation, the collection of material is not carried out, only 3 days after the termination of blood discharge can take a urogenital smear.

PCR during pregnancy

In the period of expectation of the baby many infectious diseases, sexually transmitted, are extremely dangerous for the normal development of the fetus. STDs can provoke intrauterine growth retardation, miscarriage or premature birth, congenital malformations of the child. Therefore, it is extremely important to pass an early PCR test. To pass the analysis is necessary at registration on the account - till 12 weeks.

The material is taken from the cervical canal using a special brush. The procedure is painless and does not pose a danger to the baby. Usually during pregnancy, chlamydia is analyzed by the PCR method, as well as ureaplasmosis, mycoplasmosis, cytomegalovirus, herpes, and papillomavirus. Such a complex of examinations is called PCR-6.

PCR for the diagnosis of HIV

Due to the fact that the polymerase chain reaction method is very sensitive to changes in the body and the conditions for the diagnosis, many factors can affect the result. Therefore, PCR analysis for HIV infection is not a reliable method, its effectiveness is 96-98%. In the remaining 2-4% of cases, the test gives false positive results.

But in some situations, HIV can not be avoided without PCR diagnostics. Usually it is administered to people with a false-negative ELISA result. Such indicators indicate that the person has not yet developed antibodies to the virus and they can not be detected without a multiple increase in the number. This can be achieved by conducting a blood test using a PCR method.

Also, this diagnosis is necessary for children of the first year of life who are born from an HIV-positive mother. The method is the only way to reliably determine the status of a child.

PCR for diagnosis of hepatitis

The polymerase chain reaction method allows one to detect the DNA of the hepatitis A, B, C virus long before the formation of antibodies to infection or the appearance of symptoms of the disease. Particularly effective is the analysis of PCR for hepatitis C, since in 85% of cases this disease is asymptomatic and without timely treatment passes into a chronic stage.

Timely detection of the pathogen will help avoid complications and prolonged treatment.

Comprehensive PCR examination

Complex analysis of PCR: what is it? This is a polymerase chain reaction, which involves the detection of several types of infections: mycoplasma genitalia, mycoplasma hominis, gardnerella vaginalis, candida, trichomonas, cytomegalovirus, ureaplasma urealiticom, herpes of type 1 and 2, gonorrhea, papillomavirus. The price of such diagnostics varies from 2000 to 3500 rubles. Depending on the clinic, the materials and equipment used, and also on the type of analysis: qualitative or quantitative. What is necessary in your case - the doctor will decide. In some cases, it is enough just to determine the presence of the pathogen, in others, for example, with HIV infection, an important role is played by a quantitative titer. When diagnosing all of the above pathogens, the test is called "PCR-12 analysis."

Decoding of analysis results

Decoding of the PCR analysis is not difficult. There are only 2 scales of the indicator - "positive result" and "negative result". If a pathogen is detected, doctors can confirm the presence of the disease with 99% confidence and proceed with the treatment of the patient. In the quantitative method of determining the infection in the corresponding column, the numerical value of the detected bacteria will be indicated. Only a doctor can determine the degree of the disease and prescribe the necessary treatment.

In some cases, for example, when determining the HIV infection by the PCR method, if the result is negative, it becomes necessary to conduct additional tests to confirm the results.

Where to take the analysis?

Where can I take the PCR analysis: in the state polyclinic or in a private laboratory? Unfortunately, in municipal medical institutions, equipment and methods are often obsolete. Therefore, it is better to give preference to private laboratories with modern equipment and highly qualified personnel. In addition, in a private clinic you will get results much faster.

In Moscow, many private laboratories offer PCR analysis for various infections. For example, in clinics such as Vita, Complex Clinic, Happy Family, and Uro-Pro, PCR analysis is performed. The price of the examination is from 200 rubles. For the definition of one pathogen.

It can be concluded that the diagnosis of infectious diseases using the PCR method is in most cases a quick and reliable way of detecting the pathogen in the body at early stages of infection. But in certain cases it is worthwhile choosing other methods of diagnosis. The need to conduct such a study can only be determined by a specialist. Decoding the PCR analysis also requires a professional approach. Follow the doctor's recommendations and do not hand yourself tests, which are not necessary.