Recently, a reliable, highly sensitive and fast method for diagnosing various human infectious diseases has been developed. This method is called "PCR analysis". What is it, what is its essence, what microorganisms can it reveal and how to take it correctly, we will tell in our article.
Discovery history
Invented the polymerase chain reaction (PCR) method by the American scientist Kary Mullis in 1983. Initially, the diagnostic method was patented by the Cetus Corporation, in which its creator worked. But in 1992, all rights and patents were sold to Hoffman-La Roche. After that, it turned out that similar studies were carried out in parallel and were recorded by other American biologists, such as Alice Chen, David Edgar, John Trell. In 1980, Soviet scientists A. Slyusarenko, A. Kaledin and S. Gorodetsky also de alt with this problem. Therefore, it was impossible to determine the sole copyright holder. Many prominent biochemists have made a certain contribution to the development of the polymerase chain reaction technique and have patented their innovations. At present, the analysisPCR 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 lies in the fact that with the help of a special DNA polymerase enzyme, under artificial conditions, to increase the volume of a certain microbial environment. For this, the existing DNA material is multiplied many times. Thus, in the presence of a pathogenic microorganism in the sample, its amount will be increased due to biochemical laboratory manipulations, and it will not be difficult to detect the bacterium under a microscope.
How is material research done?
Required for analysis:
- DNA matrix;
- primers connecting the ends of a piece of material;
- heat-resistant DNA polymerase enzyme;
- chemicals that make enzymes work properly;
- buffer solution necessary to create the appropriate conditions for the growth and development of DNA material.
To perform PCR, 25-30 repetitions are performed, consisting of three stages: denaturation, annealing and elongation.
For the analysis of the polymer chain reaction, a special device is used - an amplifier. Modern equipment allows you to set the necessary program for heating and cooling tubes to eliminate errors during diagnostics.
Where is diagnostics used?
The polymer chain reaction method is used in various fields of medicine:
- criminalists withit identifies genetic material such as hair, saliva or blood;
- PCR blood test helps with genotyping, for example, to detect an individual genetically inherent reaction to a certain drug;
- using this method to establish the presence of family ties between people;
- The most popular PCR method has become in medical diagnostics to determine various infectious diseases.
What infections does PCR detect?
So, medicine has long and successfully used PCR analysis. What it is, we already know. And what pathogens can be detected with it? The following infectious diseases are diagnosed by PCR method:
- hepatitis A, B, C;
- ureaplasmosis;
- candidiasis;
- chlamydia;
- mycoplasmosis;
- gardnerellosis;
- infectious mononucleosis;
- trichomoniasis;
- papillomavirus infection;
- tuberculosis;
- herpes infection types 1 and 2;
- helicobacteriosis;
- cytomegalovirus;
- diphtheria;
- salmonellosis;
- HIV infection.
Also, PCR methods are used in the diagnosis of cancer.
Method advantages
PCR diagnostics has several advantages:
- High sensitivity. Even in the presence of only a few molecules of microorganism DNA, PCR analysis determines the presence of infection. The method will help with chronic and latently occurring diseases. Often in such cases, the microorganismis otherwise uncultivated.
- Any material is suitable for research, such as saliva, blood, genital secretions, hair, epithelial cells. The most common is the analysis of blood and urogenital smear for PCR.
- No long term crop required. The automated diagnostic process allows you to get the results of the study after 4-5 hours.
- The method is almost 100% reliable. Only isolated cases of false negative results have been recorded.
- Ability to identify several types of pathogens from a single material sample. This not only speeds up the process of diagnosing the disease, but also significantly reduces material costs. Often the doctor prescribes a comprehensive PCR analysis. The price of the survey, which consists of determining six pathogens, is about 1,500 rubles.
Recommendations for preparing for analysis
In order for the results to be reliable during the PCR study, you need to take the test, following the recommendations for preliminary preparation for diagnosis:
- Before donating saliva, you should refrain from eating and taking medicine 4 hours before sampling. Immediately before the procedure, rinse your mouth with boiled water.
- The above rules should also be followed when taking a sample from the inner surface of the cheek. After rinsing, it is recommended to carry out a light skin massage to highlight the secretion of the gland.
- Urine is usually collected at home. To do this, you need to conduct a thorough toiletgenitals. Collect 50-60 ml of urine in a sterile plastic container. To ensure the purity of the material, it is recommended for women to insert a tampon into the vagina, and for men to pull the skin fold as far as possible. Don't donate during your period.
- To donate sperm, you must refrain from sexual intercourse for 3 days before sampling. Doctors also advise against visiting the sauna and taking a hot bath, drinking alcohol and spicy food. You must refrain from urinating 3 hours before the test.
- To take a urogenital smear, for example, if a PCR test is performed for chlamydia, both women and men are advised to have sexual rest for 3 days. Antibacterial drugs should not be taken 2 weeks before the analysis. For a week, you need to stop using intimate gels, ointments, vaginal suppositories, douching. 3 hours before the examination, you must refrain from urinating. During menstruation, sampling is not carried out, only 3 days after the cessation of bleeding, you can take a urogenital smear.
PCR during pregnancy
During the period of expectation of the baby, many sexually transmitted infections 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 undergo a PCR examination in early pregnancy. It is necessary to pass the analysis upon registration - up to 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, an analysis is carried out for chlamydia by the PCR method, as well as for ureaplasmosis, mycoplasmosis, cytomegalovirus, herpes, papillomavirus. Such a complex of examinations is called PCR-6.
PCR for HIV diagnosis
Due to the fact that the polymerase chain reaction method is very sensitive to changes in the body and the conditions of the diagnosis, many factors can affect the result. Therefore, PCR analysis for HIV infection is not a reliable method, its efficiency is 96–98%. In the remaining 2-4% of cases, the test gives false positive results.
But in some situations, HIV PCR diagnostics is indispensable. It is usually given to people with a false-negative ELISA result. Such indicators indicate that a person has not yet developed antibodies to the virus and they cannot be detected without a multiple increase in the number. This is exactly what can be achieved by conducting a PCR blood test.
These diagnostics are also necessary for children of the first year of life born from an HIV-positive mother. The method is the only way to reliably determine the status of a child.
PCR for diagnosing hepatitis
The polymerase chain reaction method allows detecting the DNA of the hepatitis A, B, C virus long before the formation of antibodies to the infection or the onset of symptoms of the disease. PCR analysis for hepatitis C is especially effective, since in 85% of cases this disease is asymptomatic and withouttimely treatment enters the chronic stage.
Timely detection of the pathogen will help avoid complications and long-term treatment.
Comprehensive PCR examination
Complex PCR analysis: what is it? This is an examination using the polymeric chain reaction method, which includes the determination of several types of infections simultaneously: mycoplasma genitalium, mycoplasma hominis, gardnerella vaginalis, candida, trichomonas, cytomegalovirus, ureaplasma urealiticum, herpes types 1 and 2, gonorrhea, papillomavirus. The price of such diagnostics ranges from 2000 to 3500 rubles. depending on the clinic, the materials and equipment used, as well as 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, a quantitative titer plays an important role. When diagnosing all of the above pathogens, the examination is called "PCR-12 analysis".
Transcript of analysis results
Deciphering the PCR analysis is not difficult. There are only 2 scales of the indicator - "positive result" and "negative result". When a pathogen is detected, doctors can confirm the presence of the disease with 99% certainty and begin treating the patient. With a quantitative method for determining infection, the corresponding column will indicate the numerical indicator of detected bacteria. Only a doctor can determine the extent of the disease and prescribe the necessary treatment.
In some cases, for example, when determining HIV infection by PCR, with a negative result, it becomes necessary to conduct additional examinations to confirm the obtained indicators.
Where to get tested?
Where to take a PCR test: in a public clinic or in a private laboratory? Unfortunately, in municipal medical institutions, the equipment and methods are often outdated. 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 such clinics as Vita, Complex Clinic, Happy Family, Uro-Pro, PCR analysis is carried out. The price of the examination is from 200 rubles. for identifying one pathogen.
It can be concluded that the diagnosis of infectious diseases by PCR in most cases is a fast and reliable way to detect the pathogen in the body in the early stages of infection. But still, in certain cases, it is worth choosing other diagnostic methods. Only a specialist can determine the need for such a study. Deciphering the PCR analysis also requires a professional approach. Follow your doctor's advice and don't take tests you don't need.
