Had a Negative Covid Test? Nose Swabs Are Unreliable — Try a Throat Swab

Reliability of the lateral flow tests has always been a topic of hot debate, with estimates ranging from very low reliability, to about 75-80% when used by people who know what they’re doing.

However, recently, there’s been mounting evidence that the tests are not as good at showing newer variants of covid, such as the new ‘Kraken’ variant of Omicron, which is spreading fast through the USA and is now well established in the UK. It may outcompete other strains of covid, and it seems particularly good at evading immunity.

Simon Whaley had raging covid symptoms for a full five days before he got a positive covid test on day 5 of testing. His tests on days 1 and 3 came back negative, despite nasty symptoms that were making him miserable. You can read about that here…

The Twelve Days of COVID (To the tune of the Twelve Days of Christmas)

My nieces had raging covid symptoms for three days before they got a positive test. It’s something I’ve been hearing a lot about recently. And of course, most people won’t keep testing everyday, if their initial tests come back negative, so they’ll never know they had covid.

Test sensitivity

Recently, @DrEricDing, Epidemiologist & health economist from @Harvard said:

A study on the effectiveness of lateral flow tests by Imperial College London and the University of Birmingham, “found that the devices would miss between 20 per cent and 81 per cent of positive cases in the different settings — 20 per cent at the Test and Trace centre, 29 per cent in the city-wide mass testing, and 81 per cent in the university screen testing.”

A report by Public Health England and Oxford University said that, “the Innova test had a sensitivity of 79% when used by laboratory scientists,” but the reliability of tests fell back to 73% when used by healthcare staff, and just 58% when members of the public were conducting the tests themselves.

Years ago, I saw a trial in a university where the false negatives were over 90%. I cannot find a link to that trial now. I can only guess that the university students didn’t take due care and attention with regards to following the instructions to the letter.

The levels of accuracy also depend upon the viral load of the infected individual, and the environment in which the test is conducted, says Manchester University.

Following instructions

Obviously, following the instructions properly helps. My mother-in-law likes to ditch her test as soon as the control line shows, without waiting to see if it turns positive. It’s a total waste of time doing the test if you’re not going to wait for the result before deciding it’s negative. She also forgets to mix the sample properly, doesn’t bother reading the instructions, and argues about everything.

The bottom line is, even with the greatest attention to detail, these tests are not very reliable, and high levels of human error make them even less so. However, it appears that the reliability of the lateral flow tests increases if you take a throat swab, not just a nose swab. That’s worth knowing for anyone who wants to know their status and lower the risk of infecting people around them.

Remember - the throat swab gives a more accurate reading than the nose swab, but if you combine the two, it gives you the best result. So even if your test kit is designed for the nose, try sampling the throat too!

© Susie Kearley 2023. All Rights Reserved.