PCR test for coronavirus: how is it done and when is it done?
To stop the COVID-19 pandemic is possible only by protecting the healthy population from contact with people infected with the virus as much as possible. To do this, it is necessary to quickly identify the sick and isolate them for a while. Detection is possible only by conducting tests. Today, PCR tests are used to diagnose coronavirus.
What is a PCR test for coronavirus?
The polymerase chain reaction (abbreviated as PCR) method has been used for many years to diagnose other types of viral infections, such as HIV. State laboratories for their determination by PCR have the necessary experience and equipment.
The sensitivity of the test to coronavirus showed 70 – 80%. Therefore, in some cases, you can meet with both false positive and false negative results. The accuracy of the diagnosis is also affected by the correct collection of material from the patient, its delivery to the laboratory and the analysis process itself.
What the PCR test for coronavirus shows
The PCR test gives an answer to only one question: are you now sick with coronavirus or not. It is inappropriate to do it for those who have already suffered a respiratory illness and want to find out if it was COVID-19.
If a person has been ill and wants to determine whether he is immune to the virus, a PCR study will not work. There is another type of tests for this – for antibodies.
When is the PCR test done?
Any person can do a PCR test for coronavirus, even without visible symptoms of the disease. If the virus has entered the body, testing will show it. But today it is not made for everyone. Only doctors refer to the test and the following population groups are a priority:
- citizens with signs of a cold or flu who arrived in the next 2 weeks from countries that are unfavorable for the coronavirus situation, as well as persons in contact with them;
- persons over 60 years old who have consulted a doctor with signs of SARS;
- everyone who is diagnosed with pneumonia in the coming days;
- persons with chronic diseases: cardiovascular, endocrine, oncological;
- contacts with citizens whose diagnosis of COVID-19 was confirmed.
They are also sent for analysis if a positive result is found when passing an express test.
How is PCR diagnostics of coronavirus carried out?
PCR is a direct method for the rapid diagnosis of infectious diseases, allowing the detection of specific sites for the infectious agent.
Its essence is as follows:
- A swab from the pharyngeal mucosa is taken from the patient. Before the sample is taken, the patient is not recommended to take alcohol for a day, give up food, drink, or smoke for 1 hour.
- In the resulting material, DNA fragments similar to the virus are detected. Viral DNA is isolated from a patient sample submitted to the laboratory. But when infected with a coronavirus, RNA is formed – a single chain of polynucleids. It is separated and passed to the next phase, when RNA needs to be converted into DNA. This process is called reverse transcription.
- Then the resulting DNA is multiplied (duplicated many times) using polymerase (a special enzyme). The number of repetitions can reach 40-45. Coronavirus is detected by converting DNA back into RNA.
How and when will patients know about the results?
On average, it takes from several hours to two days to receive a response in a PCR study. In case of any result, the patient is notified by the medical institution that sent him for analysis.
In case of a positive answer, a decision is made to place him in home quarantine or for treatment in a hospital, depending on the severity of the disease. The circle of persons with whom the sick person contacted in the near future must be established. They are taking material for a coronavirus test.
In case of a negative result, it is recommended to repeat the test 4 days after the first sampling of the material for analysis. It is possible that the infection has occurred, but the diagnosis was carried out too early.