Rapid COVID-19 detection tests: a more detailed guide would minimize errors

Rapid COVID-19 detection tests: a more detailed guide would minimize errors

Users of rapid antigen detection tests for COVID-19 make several mistakes when handling them and interpreting the results, Montreal researchers have found, but the situation can be remedied by providing them with more detailed instructions.

Some of the most common errors involved the amount of liquid to be used and the identification of a positive result, especially when the line that testifies to the presence of the virus is particularly faint, said Dr. Cédric Yansouni, from the Research Institute of the Center of Health at McGill University. Dr. Yansouni recalls that several countries rushed to implement these self-tests during the pandemic without first verifying whether users could use and interpret them correctly. “There was a need to determine how much we can trust the performance of people doing their own testing, and that’s what we tried to do,” explained Dr. Yansouni.

A team visited businesses where the Montreal Department of Public Health has identified at least two active cases of COVID-19. The team visited each company twice a week for two weeks. At each visit, study personnel instructed participants in nasal sampling procedures and provided either the manufacturer’s guide or a modified quick reference guide, without providing further details. In total, 1,892 tests were performed on 647 participants.

At the first self-test visit, 55.6% of participants who received the modified guideline correctly identified a weak positive test result, compared with 12.3% of participants who used the manufacturer’s guideline. Similarly, for a positive result, the correct identification rate increased from 51.5% using the manufacturer’s guide to 89.6% using the modified guide. Improvements were also seen with a strong positive result and with an invalid result. “In the amended instructions, there was a lot of emphasis on interpretation, so you don’t just show one positive and one negative example,” Yansouni said.

“We invite people to systematically ask themselves: ‘Is the test valid? Is the test negative? Is the test positive? Here are examples of barely visible lines that, despite this, are absolutely positive’. And then when we implemented that among different untrained people, we saw a dramatic difference. With an extremely simple intervention, he adds, “we were able to improve the interpretation of most of the positive results. With a simple intervention, untrained people achieve a level of reliability that (approaches) that of a professional.”

The researchers did not try to find out what caused the self-test users to interpret the results incorrectly, for example, in the presence of a faint line indicating a positive result. However, Dr. Yansouni reminds us that the human eye is not infallible. There could also be a psychological component to the phenomenon.

“The first step, he said, is to know to what extent the reading bias that is introduced by doing tests at home, because I don’t think rapid COVID tests will be the last tests that we use. The biggest challenge for the authorities is not only to implement them, but to find the correct way to communicate to the public the correct interpretation of the test, which will change according to the epidemiological situation. And that is not easy. »

At the time of the study, the rapid tests had not yet been approved by Health Canada for self-use by untrained individuals. The vaccine was just beginning to roll out and there were multiple outbreaks in the workplace. The results of this study were published by the medical journal JAMA Network Open.

Photo Credit: CANADIAN PRESS/Jeff McIntosh.

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