Thought of the Day - June 10 - Antigen Testing Limitations

Across the country we have performed over two million antigen tests; looking for signs of the SARS-COV-2 virus and thus an indication of the COVID-19 infection. As we have limited therapeutics to treat COVID-19, the main reason for the test is to highlight that the person is infectious. But this test has limitations:

1. Cost: While the test itself may only cost a few hundred dollars it is quite labour intensive. The real cost has been estimated in the thousands. If we take a conservative figure of $1,000 that means Canada has probably spent around two billion dollars on antigen testing;

2. False Negatives: One other challenge, besides, as Bonnie Henry has pointed out, the common swab test is only 70% accurate, is that timing is critical. Too early and you will get a false negative, too late and the value of the test is marginal. Remember 19 out of 20 Canadian tests come back negative;

3. False Positives: While there is only a small chance of a false positive if someone does not have COVID-19, the positive result can still appear long after the person is no longer infections, again just adding confusion in determining if a person is "Recovered";

4. Time Taken: While this issue is being addressed, in the past the combination of time taken before a person develops symptoms, seeks out a test, the 24-48 hours before the results are locally known and then 24-48 hours before they were centrally confirmed meant that a person who should be quarantined spent as much as half of their infections period without an understanding of their state.

Due to these issues, I understand why the general public has been discouraged from seeking an antigen test unless they are in a high-risk group or are significantly symptomatic. Indeed antigen testing really has limited value outside of institutional settings.

Cheers

Cliff