PCR scraping

PCR (polymerase chain reaction) is one of the most modern, fast and sensitive methods for diagnosing the presence of pathogens of infectious diseases in the human body. The principle of the method was developed by Cary Mullis in 1983, and the author was awarded the Nobel Prize in 1993 for the development of PCR analysis. It is based on the method of molecular biology, which makes it possible to achieve a multiple increase in specific nucleic acid fragments in a biological material (sample).

PCR is carried out exclusively in a laboratory that has amplification equipment that allows you to carry out all 3 stages: denaturation, annealing and polymerization in order to obtain the number of copies of the desired DNA fragment sufficient for the visual detection of pathogenic microorganisms. In addition to increasing the number of copies of DNA and RNA (this process is called amplification), PCR allows many other manipulations with genetic material (introduction of mutations, splicing of DNA fragments), and is widely used in biological and medical practice, for example, to diagnose diseases (hereditary, infectious ), to establish paternity, to clone genes, introduce mutations, isolate new genes.

PCR diagnostics is common in clinical practice and allows diagnosing the presence of long-growing pathogens without resorting to time-consuming microbiological methods, which is especially important in gynecology and urology when diagnosing urogenital sexually transmitted infections. This analysis allows you to identify pathogens in latent and latent forms.

These include chlamydia, mycoplasma, ureaplasma, trichomonas, gardnerella, candida, herpes virus and human papillomavirus. Early diagnosis of such diseases will help women avoid the appearance of malignant tumors of the cervix and other pathologies of the urogenital tract, as well as men to avoid problems with the genitourinary system.

In neonatology, PCR helps to determine the presence of infections in the fetus, such as rubella, herpes, chlamydia, or mycoplasmas. In order to minimize the risk during blood transfusion for patients with HIV status, PCR is also used for syphilis and hepatitis.

The polymerase chain reaction is used for the early diagnosis of tuberculosis. It should be noted that PCR is one of the main methods for the study of biomaterials in forensics. It is also used in experimental medicine to create genetic passports. The PCR method can detect pathogens in material obtained from environmental objects (water, soil, etc.), which is used in the analysis of products, in the pharmacological and veterinary industries.

Benefits of PCR testing

The PCR method is characterized by a number of specific advantages:

• direct determination of the causative agent of infection (100% detection of the presence of infection);
• high specificity (exclusion of false test results);
• universality and accessibility (several infections can be diagnosed);
• the speed of obtaining the results of the analysis (a maximum of 5 hours is required from the moment the material is taken);
• studies of infections during the incubation and latent period.

It is these advantages that make the PCR method irreplaceable. By resorting to this study, the pathogen can be detected in soil, food and water.

Limitations of the PCR Method

Despite the undeniable advantages, PCR has a number of drawbacks, but they are not so significant as to reduce the status of using the method for clinical diagnostics. Among the restrictions are the following:

• detection of a dead infection (non-compliance with the time after treatment for a specific disease, if less than 2 months have passed, the remains of dead microorganisms can be found in the sample);
• the occurrence of cross-reactions (a DNA fragment taken for analysis may be present in other microorganisms, which can lead to a false result);
• mutations in microorganisms.

In order to minimize possible risks, standards for PCR research have been developed, which include checking for cross-reactions and studying known strains of infection.

Research stages

The polymerase chain reaction is carried out in an amplifier – a device that provides periodic cooling and heating of test tubes, usually with an accuracy of at least 0,1 ° C. The addition of specific enzymes can increase the yield of the PCR reaction. The material may be scraping from the urethra, cervical canal, mucous membranes of the respiratory tract, conjunctiva and other biological fluids. The sampling procedure is carried out using special tools; for urine analysis, the first morning portion is collected in a clean sterile container.

This method allows you to identify genitourinary infections. For the diagnosis of tuberculosis, mycoplasmosis and chlamydia in respiratory diseases, sputum is used, which is placed in a test tube. To determine HIV infection, herpes and hepatitis, venous blood is taken for analysis.

A saliva sample is taken in the morning on an empty stomach, prostate juice, amniotic fluid, cerebrospinal and pleural fluid are taken by puncture. It is possible to store the collected material for 2 hours, if it is necessary to increase the storage time, test tubes with liquids are placed in a refrigerator with a temperature not higher than 8 ° C for one day.

Significance of the results of the PCR study

The value of the results can be positive or negative. If the tests are positive, then certain pathogens are found in the patient’s body. If negative, then there are no studied organisms.

It should be noted that the attending physician should deal with all transcripts of studies. He will correctly determine the quantitative result after the polymerase chain reaction and, based on the conclusion about the activity of the infection, prescribe the necessary treatment for the patient.

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