The at-home antigen test: What do experts think, and how do you use them?
Scientific opinion divided on reliability of home Covid-19 tests
A Covid 19 antigen test. File photograph : Laura Hutton/The Irish Times
According to the antigen tests which went on sale this week in Lidl, it is 98.72 per cent accurate for detecting if somebody has Covid-19.
This is a bold claim and not one supported by the Chief Medical Officer Dr Tony Holohan.
At Friday’s National Public Health Emergency Team (Nphet) briefing, Dr Holohan said the accuracy of these tests is about 50 per cent in “the hands of trained professionals”.
Antigen testing has a role he suggested, but “in strictly controlled circumstances where we know the test is going to work”.
He then raised the possibility of a shopper going to Lidl to buy a pound of sausages, charcoal for the barbecue and an antigen test.
Lidl Ireland responded with a tweet. “Weekend Super Savers! Pick up a pound of sausages, charcoal for the BBQ and antigen tests for €31”.
Professor Mark Ferguson, director general of Science Foundation Ireland, and chief scientific advisor to the Government, has a different take on home antigen tests.
The co-author of a Government-sponsored report on rapid antigen testing, he gave a defence of them at the Oireachtas committee on transport this week.
“There are plenty of good videos. Taking the sample is very easy to do. Reading the test is very important and that can be aided with a photograph. Selecting the right commercial test kit is also important. Of course, no test is infallible,” he said.
“There are about one in 1,000 false positives with an antigen test, while there are false negatives as well and people need to be educated about that. They need to be told that the test is not perfect but that is true of almost any test.”
He likened the conventional PCR Covid-19 test to a Rolls Royce car, but who needs a Rolls Royce when it burns so much petrol, he suggested.
Prof Ferguson said home antigen tests are perfectly fine and usually accurate in determining if someone is infectious with Covid-19 at the moment of testing.
Using the supermarket antigen test
I can’t vouch for the accuracy of the Lidl antigen test, but I can vouch for its ease of use.
The instructions leaflet in eight languages could fill a coffee table. It is daunting at first glance, but there is an instructions video online.
The kits cost €25 each so the cost of each test is €5.
In each box there are five sterile swabs, five extraction tubes, five sample buffers, five rapid antigen test cards and a tubeholder.
You put the sample buffer into the extraction tube. Then you take a swab in both nostrils and place the swab into the sample buffer. You close the lid on the extraction tube. The last part of the procedure is to dab the buffer with the swab sample into a well in the antigen test card and then you wait.
It states that you should receive a response within 15 to 20 minutes, but within four minutes my sample was already showing a negative pink line in the test card and it never changed.
The Lidl test kit is made by Boson, a Chinese biotech company. It comes with 14 separate caveats warning that, if the proper procedure is not followed, the test may prove to be inaccurate.
It states that someone who tests positive should go to a doctor. Furthermore it warns that the antigen test is less likely to show a positive test after five to seven days of illness as it is when a person first exhibits symptoms.
The Xiamen Boson Biotech Co, Rapid SARS-CoV-2 Antigen Test card was one of 16 antigen tests approved in February for use in the European Union. It is in widespread use in France, Germany, Belgium and Bulgaria.