Testing is being offered to more communities outside of hospital and people aren’t just getting tested when they have symptoms. Some say that this is leading to more ‘false positives’ in which people test positive for coronavirus but are clear because the test has not been performed properly. There’s also concern that people are being cleared of having the virus but, in fact, the testing hasn’t spotted their infection.

This is happening but not on the scale that has been talked about on social media sites. The rising number of positive tests reflects the extent to which the virus is spreading. Remember, no test is 100% accurate – there will always be some who test positive when they don’t have the disease, or negative when they do have it, and a test is just a snap-shot in time. However, experts at Cambridge University’s Medical Research Council’s Biostatistics Unit believe the proportion of false positives could be as low as 1%1.

False positives vary hugely depending on who is being tested. Most undergoing tests at drive-through centres, for instance, are people with symptoms, live in virus hot-spots or are in care homes. They are not a random sample of the public but people who are much more likely to have the virus. If you are worried, then it’s best to assume that you could be at risk from contracting or spreading the virus if you mix amongst people who are outside of your household. So always be diligent when it comes to distancing and follow the correct hygiene advice – washing hands and covering the face.

When it comes to testing there’s a confusing array of words. Experts often talk about nasopharyngeal swabs. These are long, flexible sticks tipped with a soft swab, inserted deep into the nose to get samples from the space where the nasal cavity meets the throat. Other swabs – oral, throat or nasal – don’t go as deep.

And then there are the test themselves. An antibody test detects antibodies specific to the coronavirus, which appear in the blood about a week after infection. Because antibodies take so long to develop, tests can’t reliably diagnose ongoing infections but can identify people who have been exposed to coronavirus.

There are also antigen tests which detect bits of coronavirus proteins called antigens in saliva. These are less accurate because they’re not looking for the genetic material of the virus. They’re also called ‘lateral flow tests’, handheld kits which give a result in less than half an hour. They aren’t as effective as laboratory kits so if you have a relatively mild infection, you may not get the positive result you should – 1 in 5 are wrongly negative. However, in areas without large laboratory facilities, they are still useful because if you test positive it is likely to be accurate.

You can get a test by going online or calling 119 if you’re in England, Wales or Northern Ireland and 0300 303 2713 if you’re in Scotland, at which point you will be advised where to go. These swab tests are then sent to a laboratory and you’ll hear back within three days. In hospitals, turnaround times are much faster.

Alternatively, you can pay up to £200 for a private test to see if you’re infected or about half of that price to check if you have antibodies, suggesting you were infected in the past and now have some protection. Make sure any tests you pay for have a special ‘CE’ mark which proves they meet legal standards. However, antibody tests don’t work for everyone – some who have had coronavirus do not have antibodies.

In association with communications consultancy, GF Media

 

References

  1. https://www.mrc-bsu.cam.ac.uk/tackling-covid-19/nowcasting-and-forecasting-of-covid-19/