On April 23, the Ministry of Food and Drug Safety has conditionally approved two types of COVID-19 self-examination kits: the STANDARD Q COVID-19 Ag Home Test by SD BIOSENSOR and Humasis COVID-19 Ag Home Test by Humasis. Meanwhile, the disease control authorities emphasized that after using the self-examination kit, one should get the PCR test to verify the negative response. They also pointed out that one should not determine whether one is positive/negative to COVID-19 by only using the self-examination kits. The Central Disease Control Headquarters announced, “The self-examination kit approved this time has the advantage of convenience, but also the disadvantage of low accuracy. Therefore, it is necessary to familiarize yourself with the product instructions and use them carefully on the premise that you thoroughly comply with the quarantine rules.” They also reiterated that the kits should only be used as an ancillary means.
Here is how to use the self-examination kit. First, insert a sterile swab into the nostril so that the swab reaches the depth equal to the distance from the nostrils to the outer opening of the ear. Rotate the swab three to four times. Next, insert the swab into an extraction buffer tube. Squeeze the sides of the tube to extract the liquid from the swab. Apply three drops of the extracted specimen to the specimen well of the test device and wait for about 15 to 30 minutes. The specimen well has two mouse monoclonal anti-SARS-CoV-2 antibody coated lines, “C” Control line, and “T” Test line. Both C and T in the result window are not visible before applying any specimens. If SARS-CoV-2 antigens are present in the specimen, a colored test line would be visible in the result window. If the antigens are not present, then no color appears in the test line. The control line is used for procedural control, and should always appear if the test procedure is performed properly and the test reagents of the control line are working. If no color appears in the control line, the test is invalid and one should take a new trial.
The diagnostic methods for COVID-19 are RT-PCR, viral culture, and antibody tests. The self-examination kit was produced by the rapid antigen test method among antibody tests. Unlike the other two tests, the rapid antigen test method is relatively easy and convenient because it detects proteins caused by the viruses, not viruses themselves. However, this diagnostic method has detection limits. According to the U.S. Food and Drug Administration, unlike the RT-PCR test, which can produce results with just about 180 to 1,000 viruses, the STANDARD Q COVID-19 Ag Home Test requires two million viruses.
Experts are showing concerns about the kit’s low accuracy. The accuracy of the diagnostic test is judged by sensitivity and specificity. Sensitivity measures how often a test correctly generates a positive result for people who have the condition tested. Specificity measures a test’s ability to correctly generate a negative result for people who do not have the condition tested. According to the Seoul National University Hospital, STANDARD Q COVID-19 Ag Test tested on 98 positive samples showed only 17.5% sensitivity. In December 2020, the Korean Society for Laboratory Medicine verified the same kit with 680 samples, and the sensitivity was low at 29%. On April 12, the temporary screening center in the Seoul metropolitan area conducted tests on 48 positive cases, and 16 cases were false positive, showing 33.3% specificity. One should be aware of the low accuracy of the self-examination kits and follow the quarantine rules without fully trusting the test results.