Mailbox: Why do COVID tests need a nasal swab?

James has been in touch to ask: Why does the COVID lateral flow test require using a rather unpleasant throat or nasal swab ? Why won't spitting saliva into the buffered solution work in the test strips? Chris Smith has the answer...

Chris - Yeah people have likened having these nose and throat swabs to having a brain biopsy. The answer is - reproducibility. Saliva is, in certain cases, a very good measure and marker of infection. If you have something that grows in your nose, in your throat, where saliva washes around, you can use saliva to get the genetic information and sometimes the organism itself or its antigens, the things it makes when it grows, and test for them. But it's difficult and inconsistent. And when people have done studies on coronaviruses, they found that because of the other stuff which can be present in saliva and because people are all different, the areas that they get the saliva from, the volume of saliva they produce and so on, it makes it very hard to produce a test which is consistent and reliable. Whereas a throat swab and a nose swab combined do tend to produce a more reliable, consistent sample, which is therefore easier to test. So at the moment, it's down to practicality and reliability, but watch this space because in the long term we all know spitting into a tube is a lot more attractive than doing a brain biopsy.