The need to learn the correct usage of the COVID-19 self-test kit is growing.



To increase the accuracy of the self-test, there are cases where a self-test swab is forcefully inserted into the nose, but this is not recommended.



According to the Ministry of Food and Drug Safety (MFDS), when performing a self-exam, the cotton swab should be rubbed in a circular motion 10 times with the swab touching the wall of the nostrils 1.5 to 2 cm deep.



An official from the Ministry of Food and Drug Safety said, "The self-test is a method of collecting the virus from the nasal mucosa cells with a cotton swab, so you only need to use the cotton swab to touch the surface of the mucous membrane. “, he explained.



Because the rapid antigen test method and PCR used for self-testing are different, it is difficult to expect PCR-level accuracy no matter how many nasal samples are collected.



In the initial stage of infection, the accuracy is low, and there is a limit that sensitivity increases when used within a week from the onset of symptoms when a lot of virus is released.



Ultimately, the best thing an individual can do is follow the instructions for use of the self-test kit.



All of the self-test kits approved by the Ministry of Food and Drug Safety in Korea have met the criteria of 90% sensitivity and 99% specificity in clinical performance tests, but in the field, about 1 in 4 people are not actually infected and are found to be 'fake-positive'. Comes out.



This is because sensitivity and specificity, which are used as criteria for accuracy at the time of approval, are different concepts from the 'positive predictive value' actually confirmed in screening laboratory tests.



In the clinical performance test, positive and negative diagnoses are confirmed while the infected and non-infected individuals are identified.



Therefore, this value should be regarded as a statistic from a controlled experimental environment.



On the other hand, the positive predictive value refers to the percentage of people who are positively infected by PCR test, as a result of self-tests by people who do not know whether they are infected at the actual site.



This number fluctuates depending on the status of the infection, increasing when more people are infected and lower when there are few people infected.



According to the Ministry of Food and Drug Safety, assuming that 3 out of 100 Koreans are infected, if a domestically approved product is used in the field, the positive predictive value, that is, the ratio of true infections among those who test positive with the self-test kit is about 73.6%.



With 10 out of 100 infected, this rate rises to 90.9%.



If 1 in 100 people are infected, the positive predictive value is lowered to 47.6%.



Accordingly, experts recommend that even the same rapid antigen test be tested at a respiratory clinic, rather than using a self-test kit.