Among modern diagnostic methods, one of the most accurate and informative methods is a smear on PCR. The advantage of the polymerase chain reaction method is the ability to use any biological material. Most often, a scraping for laboratory research is taken from the genitals of men and women in order to detect and prevent sexually transmitted infections.
What is this analysis?
The PCR method is used not only in medicine. It is used in archeology, genetics, forensics. The developer of this type of diagnosis is the American chemist Cary Mullys, a Nobel laureate. By the way, he received the most prestigious international award for his discovery of the PCR method.
Thanks to the polymerase chain reaction , scientists have the opportunity to determine the similarity of DNA, to establish paternity and family ties. Nevertheless, the main purpose of a smear by PCR is considered to be the diagnosis of infectious diseases in humans.
Polymerase chain reaction is a highly accurate method of molecular genetic research, the conduct of which allows the detection of viral, genetic and hereditary pathologies. The advantage of this technique is the ability to determine pathogens not only in the acute or chronic stage of the disease, but also in the incubation period, that is, before the first symptoms of the pathology appear.
A smear on PCR never gives a false positive response. This distinguishes this diagnostic method from others. If there is no infection in the body, the patient will not get a positive result - there is no doubt about it. Today, the analysis for polymerase chain reaction is passed in order to determine the type of pathogen and its amount.
Advantages of PCR
None of the research methods is able to find the pathogen directly in the gene contained in the studied materials. PCR is the most accurate and reliable analysis for sexually transmitted diseases and latent viruses in the body. Unlike other diagnostic methods, the analysis of the polymer chain reaction has several advantages:
- It aims to detect the causative agent of the infection;
- It is universal because it allows you to identify several types of infectious agents at once;
- however, it is sufficient to use only one biological sample of the patient;
- possesses hypersensitivity, due to which the probability of possible cross-reactions is zero.
Compared to bacteriological culture, a PCR smear is considered the most reliable and fastest diagnostic method. The laboratory diagnostic procedure itself does not take more than four hours. At least seven days are required to obtain the result of a bacterial sowing. The essence of this method is as follows: a sample of the biomaterial is placed in a favorable environment and observe the activity of pathogens, if any, throughout the study period.
PCR is suitable for identifying which infections
PCR smear analysis can reveal any number of infectious pathogens in the body, including “hidden” viruses that do not show any symptoms for a long time. This diagnostic method is used when it is necessary to confirm or deny the presence of the patient:
- viral hepatitis;
- ureaplasmosis;
- genital tract chlamydia;
- human papillomavirus;
- herpes
- malignant cells;
- mycoplasmosis;
- vaginosis;
- mononucleosis;
- trichomoniasis;
- HIV infection.
Blood, saliva, sputum, and urine are used as the test material for PCR analysis. Before the procedure for taking a scraping, the patient needs to prepare for it. The attending physician will inform the patient about how to prepare before analyzing a PCR smear. As a rule, specialists conduct appropriate consultations with patients. For example, blood is donated on an empty stomach, and immediately before a cervical scraping, it is undesirable to carry out hygiene procedures.
Samples for research
Almost any human biological fluid can be the material for PCR analysis. Foreign DNA of pathogens can penetrate into any environment. Most often, blood and its individual components (plasma or serum) are used as a sample for research. RNA of viral hepatitis, herpes simplex, cytomegalovirus, HIV can be present in liquid tissue.
Broad indications for the study are biological fluids. These include:
- prostate juice;
- sperm;
- vaginal secretion;
- spinal (cerebrospinal fluid);
- amniotic;
- bronchoalveolar lavage;
- joint fluid;
- saliva.
To diagnose sexually transmitted diseases such as gonorrhea, chlamydia, mycoplasmosis, ureaplasmosis, trichomoniasis, gardnerellosis, herpetic forms, etc., patients take epithelial scrapings from the mucous membranes. In men, a PCR smear is taken from the urethra, and in women, from the vagina or cervix.
A separate category is biopsy specimens. Most often, biopsy samples are examined in order to determine the nature of the neoplasm, confirm its malignancy. Biopsies of the stomach and duodenum are required to detect the Helicobacter pylori bacteria and its quantitative load.
Urine as a biomaterial is used for infectious lesions of the urinary system. In men, a PCR smear is often replaced by a urinalysis, since the urethra in the stronger sex is a universal element of the genitourinary tract.
To diagnose tuberculosis and obstructive pulmonary diseases, sputum is examined. The material can be collected in a sterile vial (15-20 ml) or take a swab from the throat. PCR analysis is also used to detect complicated forms of mycoplasmosis and chlamydia - in the absence of treatment and other adverse factors, these types of infections can affect the human respiratory system.
How to take biological fluids for PCR: general rules
The preparation method depends on what kind of biomaterial must be submitted for research:
- If a saliva sample is required for analysis, the procedure is performed on an empty stomach. Do not take medications a few hours before the study. In addition, it is undesirable to drink a lot of liquid, especially hot, so as not to disrupt the natural composition of the microflora of the oral cavity.
- Urine for PCR should be collected in the morning. To do this, prepare a sterile container and wash thoroughly. The material should not contain impurities, therefore, men should urinate the foreskin during urination, and women should close the vagina with a cotton swab.
- Three days before the delivery of sperm, a man needs to refuse sex. During the preparation period, it is undesirable to visit the bath, take a hot bath, drink alcohol, spicy dishes. Before collecting biomaterial, you can not urinate, so it is advisable to limit fluid intake a day before the analysis.
- Blood, as already noted, must be donated in the morning, on an empty stomach. 2-3 days before the analysis, it is advisable to refuse fatty foods, alcohol and potent medicines.
Indications for scraping in women
If a sexually transmitted disease is suspected, the doctor may prescribe a woman a smear for PCR. In laboratories that belong to budget clinics, such tests usually do not. Before choosing a place for research, you need to make sure that they carry out the necessary diagnostics.
Most of the sexually transmitted diseases may not manifest themselves for several months, so the absence of symptoms is not a guarantee that the girl is not infected. Being a carrier of infection and not knowing about the disease, a woman can not only infect a partner, but also miss the time for successful treatment. Sexually transmitted diseases can lead to infertility, inflammation of the pelvic organs and other complications.
A PCR smear for an infection is prescribed to a woman if there has been contact with an unfamiliar partner. If the venereal status of the latter is unknown, then there is a risk of infection. Putting a smear on PCR is advisable if:
- the woman doubts the “purity” of her new partner, since a condom was not used during intercourse;
- during the year the woman had several sexual partners;
- the patient has previously been diagnosed with a sexually transmitted disease;
- pregnancy has come.
Screening for genital infections is mandatory for expectant mothers, since some of them, even if they proceed secretly and do not make themselves felt, can pose a serious risk to the life and health of the fetus.
Smear procedure
A scraping in women is taken by a gynecologist. The very procedure for taking a scraping for a polymerase chain reaction is no different from a conventional gynecological examination for vaginal flora. The procedure for taking a PCR smear for chlamydia, trichomoniasis, human papillomavirus, gonorrhea and other genital infections occurs according to the standard scheme:
- The patient is preparing for the procedure and takes a place on the gynecological chair.
- To collect the material, the gynecologist puts on disposable sterile gloves and examines the external genitalia.
- Next, a special dilator is inserted into the woman's vagina, which allows you to examine the internal epithelium with a mirror.
- A special brush is used to collect biomaterial, which does not have absorbent properties and is not able to damage the mucous membranes. With its help, a scraping is taken from the cervical canal, the walls of the vagina. An ordinary cotton swab is not suitable for this purpose.
- The used medical device containing vaginal secretion is inserted into a test tube, closed and sent to the laboratory.
The procedure for taking a scraping is usually painless, but sometimes patients experience discomfort due to contact of the sensitive mucosa with gynecological instruments. Pain in the process of taking biomaterial can indicate an ongoing inflammatory process.
Preparing women for a smear test
- It is impossible to enter into an intimate relationship before the procedure - at least two days should pass after the last contact.
- If a woman is being treated with antibiotics or using vaginal suppositories, three weeks before taking a PCR smear, the course of therapy must be completed. Otherwise, the result of the analysis may be false.
- During menstruation, a smear is not taken.
- Do not douche or use an antibacterial soap immediately before taking the biomaterial.
- Before the procedure, you can not visit the toilet, the last time you can urinate three hours before the procedure.
Features of the preparation and conduct of the procedure in men
As already mentioned, a PCR smear in men is taken from the urethra. To obtain the necessary biomaterial, the urologist uses a special thin probe and inserts it to a depth of 3-4 cm. The process of taking a PCR smear for ureaplasma, gonorrhea, and other common pathogens can cause pain and considerable discomfort. But you have to tolerate. Often in men, a smear on PCR causes a burning sensation and itching, therefore, before the introduction of the probe, in order to reduce the discomfort, patients are recommended to massage the urethra. The step-by-step procedure for taking a scraping looks like this:
- A man frees the genitals from clothes.
- Before inserting the probe into the urethra, the doctor puts on disposable gloves and performs a visual examination of the skin, mucous membranes for rashes.
- Then, with the help of a tool, the urologist takes a smear by PCR from the urethra. The probe is inserted 3-4 cm deep into the urethra and scrolls several times.
- After removing the probe, the doctor makes a smear on a glass slide, which will subsequently be sent to the laboratory.
In addition to painful sensations, the procedure for taking a scraping causes psychological discomfort in men. Those who visit the urologist regularly do not have such problems. In addition, proper preparation for a PCR smear is important. It consists in observing the following conditions:
- A few days before the analysis, a man needs to abandon intimate relationships.
- A smear is taken in the morning.
- Before the procedure, a man does not need to conduct genital hygiene, it is best to take a shower in the evening.
- Three hours before taking a sample of biomaterial, you should not use the toilet.
As with women, potent drugs can distort the result of a polymerase chain reaction test.
How PCR assays are decoded
In principle, in order to understand the results of a laboratory test for the polymerase chain reaction, you do not need to have a medical education. Deciphering the expert opinion is quite simple. The answers given to the patient in their arms contain information about the type of infection. If the pathogen is detected, a positive result will be noted in the conclusion. It indicates the presence of the DNA or RNA of the virus in the body of the person being studied.
For the effective treatment of certain diseases, it is necessary to have accurate data on the quantitative load, which means the presence of RNA copies of the pathogen per 1 ml of blood. To a greater extent, the determination of the quantitative load is important in diseases provoked by opportunistic microflora, since infectious agents are activated and negatively affect the human body only if their number exceeds the established thresholds. Such a PCR analysis is of particular importance for the preparation of a treatment plan and for monitoring the dynamics of patients infected with viral hepatitis or HIV infection.
How long to wait for an answer
Studies on PCR are characterized by maximum accuracy, specificity and sensitivity. A smear on the polymerase chain reaction allows you to find out if there is a specific type of infection in the body of the subject, to determine its strain and the number of RNA copies. The PCR method allows the identification of the pathogen even with a minimal content of virus DNA in the presented samples of the biomaterial.
The timing of the analysis depends largely on which of the existing methods of polymerase chain reaction is used in a particular laboratory. The easiest way to study biological material is considered microscopic. Usually this research method does not take much time. For urgency, patients have to pay extra, but if for any reason there is a need for an emergency study, the results can be given to the patient in his arms after an hour. The quickest answers to the tests are received by those who turn to specialized medical facilities equipped with their own laboratory. Otherwise, it is necessary to take into account the time that will be spent on the delivery of biomaterial.
PCR smear prices in Moscow
The final cost of the analysis will depend on which infection the patient needs to be tested. In Moscow, the following prices are set for laboratory tests by PCR:
- sexually transmitted diseases - the analysis is performed on average in 1-2 days, the cost is 300-500 rubles. (for the detection of one pathogen);
- the same terms and prices are set for PCR diagnostics of the Epstein-Barr virus, human papilloma, herpes, cytomegalovirus infection;
- screening for hepatitis A, B, C, D, G will cost the patient 650-800 rubles., To clarify the quantitative load will have to pay another 2000 rubles. (it takes 4-5 days to complete the study);
- confirmation of the presence in the gastric or intestinal biopsy of the bacteria Helicobacter pylori (Helicobacter pylori) - 400-600 rubles;
- HIV antibodies and antigens - 400-500 rubles;
- the amount of HIV RNA in blood samples is more than 10 thousand rubles.
In order to save money, doctors recommend choosing analysis packages - such studies are cheaper. Discounted services are provided in most network clinics where they are tested using the PCR method (“SM-Clinic”, “Invitro”, “ON-Clinic”) and multidisciplinary medical centers.
If pathogenic pathogens are found in the smear, do not despair. The main thing is to start therapy as soon as possible. Today, there are many drugs, thanks to which even patients with incurable diseases have every chance of high quality and normal life expectancy. The choice of treatment tactics should be carried out by a doctor. Self-medication for infectious diseases is unacceptable.