Not so long ago, a reliable, highly sensitive and quick method for diagnosing various human infectious diseases was developed. This method is called "PCR analysis." What is it, what is its essence, what can it reveal microorganisms and how to donate it correctly, we will tell in our article.
Discovery story
The American scientist Carey Mullis invented the method of polymerase chain reaction (PCR) in 1983. Initially, the diagnostic method was patented by Cetus Corporation, in which its creator worked. But in 1992, all rights and patents were sold to Hoffman-La Roche. After which it turned out that similar studies were conducted in parallel and were recorded by other American biologists, such as Alice Chen, David Edgar, John Trel. In 1980, Soviet scientists A. Slyusarenko, A. Kaledin and S. Gorodetsky also dealt with this problem . Therefore, it turned out to be impossible to determine the sole copyright holder. Many prominent biochemists made a certain contribution to the development of polymerase cericidal reaction methods and patented their innovations. Currently, 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 lies in the fact that using a special enzyme, DNA polymerase under artificial conditions to increase the volume of a certain microbial environment. To do this, multiply the available DNA material. Thus, in the presence of a pathogenic microorganism in the sample, its quantity will be increased due to biochemical laboratory manipulations, and it will not be difficult to detect the bacterium through a microscope.
How is material examined?
For the analysis required:
- DNA template;
- primers connecting the ends of the fragment of the material;
- heat-resistant DNA polymerase enzyme;
- chemicals that ensure the proper functioning of enzymes;
- 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.
To analyze the polymezar 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 the diagnosis.
Where is the diagnosis used?
The polymezar chain reaction method is used in various fields of medicine:
- forensic scientists use it to identify genetic material, such as hair, saliva, or blood;
- a PCR blood test helps with genotyping, for example, to detect an individual genetically embedded reaction to a particular drug;
- using this method, the presence of family ties between people is established;
- 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 is it, we have already learned. And what pathogens can be detected with its help? The following infectious diseases are diagnosed by PCR:
- hepatitis A, B, C;
- ureaplasmosis;
- candidiasis;
- chlamydia
- mycoplasmosis;
- gardnerellosis;
- Infectious mononucleosis;
- trichomoniasis;
- papillomavirus infection;
- tuberculosis;
- herpes infection of the 1st and 2nd types;
- helicobacteriosis;
- cytomegalovirus;
- diphtheria;
- salmonellosis;
- HIV infection.
Also, PCR methods are used in the diagnosis of cancer.
Method Advantages
Diagnosis of PCR has several advantages:
- High sensitivity. Even with only a few DNA molecules of the microorganism, PCR analysis determines the presence of infection. The method will help with chronic and latent diseases. Often in such cases, the microorganism is uncultivated in other ways.
- Any material is suitable for research, for example, saliva, blood, sexual secretions, hair, epithelial cells. The most common is a blood and urogenital smear test for PCR.
- Long-term crop production is not required. The automated diagnostic process allows you to get the results of the study after 4-5 hours.
- The method is almost completely reliable. Only isolated cases of a false negative result were recorded.
- The ability to identify several types of pathogens from a single sample of material. 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 cost of the examination, consisting of a determination of six pathogens, is about 1,500 rubles.
Analysis Preparation Guidelines
In order for the results to be reliable when conducting a PCR study, you need to pass an analysis, observing the recommendations for preliminary preparation for diagnosis:
- Before giving saliva, you should refrain from eating food and medicine 4 hours before taking the material. Rinse your mouth with boiled water immediately before the procedure.
- The above rules should be followed when taking a sample from the inner surface of the cheek. After rinsing, a light massage of the skin is recommended to highlight the secretion of the gland.
- Urine is usually collected at home. To do this, you need to conduct a thorough toilet of the genitals. In a sterile plastic container, collect 50-60 ml of urine. To ensure the purity of the material, it is recommended for women to insert a tampon into the vagina, and for men to pull off the skin fold as much as possible. You can not take the material during menstrual flow.
- To give sperm, you need to refrain from intercourse for 3 days before taking the material. Doctors also advise you to stop visiting the sauna and taking a hot bath, drinking alcohol and spicy foods. 3 hours before the analysis, you need to refrain from urinating.
- For delivery of an urogenital smear, for example, if PCR chlamydia is analyzed, both women and men are recommended to have sexual rest for 3 days. 2 weeks before the analysis, antibacterial drugs should not be taken. For a week, you need to stop using intimate gels, ointments, vaginal suppositories, douching. 3 hours before the study, you need to refrain from urinating. During menstruation, material is not taken, only 3 days after the cessation of blood discharge, 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 cause intrauterine growth retardation, miscarriage or premature birth, or congenital malformations of the baby. Therefore, it is extremely important to undergo a PCR examination in early pregnancy. An analysis must be submitted 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 performed on chlamydia by the PCR method, as well as on ureaplasmosis, mycoplasmosis, cytomegalovirus, herpes, papillomavirus. Such a survey complex 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 diagnostic conditions, many factors can affect the result. Therefore, analysis of PCR 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, PCR diagnosis of HIV is not enough. Usually it is carried out to people with a false negative result of ELISA. Such indicators indicate that the 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 performing a PCR blood test.
Such a diagnosis is 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 the child.
PCR for the diagnosis of hepatitis
The polymerase chain reaction method allows you to detect the DNA of hepatitis A, B, C virus long before the formation of antibodies to infection or the appearance of symptoms of the disease. An analysis of PCR for hepatitis C is especially effective, since in 85% of cases such a disease is asymptomatic and without timely treatment passes into the chronic stage.
Timely detection of the pathogen will help to avoid complications and prolonged treatment.
Comprehensive PCR examination
Comprehensive PCR analysis: what is it? This is a polymezar chain reaction test, which includes the determination of several types of infections at the same time: mycoplasma genitalia, mycoplasma hominis, gardnerella vaginalis, candida, trichomonads, cytomegalovirus, ureaplasma urealitum, herpes simplex type 1 and type 2, gonorrhea, papillomas. The price of such a diagnosis ranges from 2000 to 3500 rubles. depending on the clinic, materials and equipment used, as well as on the type of analysis: qualitative or quantitative. Which 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 the quantitative titer. In the diagnosis of all of the above pathogens, the examination is called "PCR-12 analysis."
Decryption of analysis results
Deciphering the PCR analysis is not difficult. There are only 2 indicator scales - “positive result” and “negative result”. If a pathogen is detected, doctors can confirm the presence of the disease with 99% certainty and proceed to treat the patient. With a quantitative method for determining infection, the numerical indicator of the detected bacteria will be indicated in the corresponding column. Only a doctor can determine the degree of the disease and prescribe the necessary treatment.
In some cases, for example, when determining HIV infection by PCR, with a negative result, it is necessary to conduct additional examinations to confirm the obtained indicators.
Where to pass the analysis?
Where to take a PCR analysis: in a public health 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 clinics such as Vita, Integrated Clinic, Happy Family, Uro-Pro, PCR analysis is performed. The examination price is from 200 rubles. for determining one pathogen.
It can be concluded that the diagnosis of infectious diseases by PCR in most cases is a quick 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 PCR analysis also requires a professional approach. Follow the doctor’s recommendations and don’t take your own tests, which are not necessary.