Senior Lecturer of the Department of Microbiology and Immunology of the Surgical Clinic, Head of the Clinical and Diagnostic Laboratory of the Azerbaijan Medical University, Javer Khajis, in an interview with Haqqin.az spoke about the methods of testing the COVID-19 virus.
– What methods are used when testing to COVID-19 virus?
– Since COVID-19 is a viral disease, the same methods are used to identify it as when identifying other viruses. Since virology is a more microbiological research method, sowing method is considered to be a gold standard. When screening viruses, a molecular genetic method is used, the serological method and tests for antigens, which we call PCR (polymerase chain reaction). Against the COVID-19 virus in the blood forms of IgG (immunoglobulin G) and IgM (immunoglobulin M) are formed. Originally, IgM is formed in the blood – these are antibodies that are formed in the acute period of the disease. Later begins to form an IGG. And from the 10-14th day, IGM disease turns into IGG and circulates in the blood. IgG is formed in the body against COVID-19, that is, an immune response is formed.
– As you know, it is possible to determine the presence of the COVID-19 virus in the body using PCR testing. Sometimes citizens hand over analyzes in different clinics and cannot enter the system as a patient if the results are positive. We also received a number of appeals in connection with this. What is the difference between these analyzes?
– Antigens tests are also used when determining the COVID-19 virus. This is a method that is often called express testing. Citizens confuse it with PCR test, or in hospitals, where they hand over the smears, the difference between these strokes is not registered. What is the difference: in both methods of surveys take strokes from the nasopharynx and from the mouth. Antigenic tests are dissolved in a special buffer solution. This method uses special card tests. This solution is added to the test and receive a response in about 10 minutes. Each method has sensitivity indicators, specificity. The most accurate method of testing to coronavirus is PCR testing, its accuracy is 90-92%, while the rapid test on the antigen has a slight level below. In a statement, WHO also notes that the results obtained by other methods must be confirmed by PCR analysis.
– We are confronted with such appeals of citizens. The citizen has characteristic signs of COVID-19, but the reaction to PCR is negative. How can this be explained?
– there are pre-analytical factors that can affect the results of the tests. In general, in world practice, the influence of pre-analytic factors on the analysis result is noted as 70 percent.
– But what are the constant positive results in PCR tests?