There is a lot of talk about making a simple, cheap test that could be used at home to check whether we have been already exposed to the COVID-19. How is this test different from the one we already have and will we be able to use it soon?
There is a lot of excitement around the announcement that 3.5 million coronavirus testing kits are on their way to the UK, with the possibility of them to be available to buy from Amazon or Boots within days. Although these tests are rapidly improving, they need to be optimised to make sure they are as reliable as our standard COVID-19 tests.
Current COVID-19 tests use samples from nose or throat swabs and detect the presence of the virus itself. Coronaviruses contain RNA (a genetic material similar to DNA), and because we’ve known the coronavirus RNA sequence since January, we can look for that exact bit of RNA in the sample. This RNA test is relatively straightforward to do (any biologist could do it in a standard lab) and uses a common lab technique called PCR. This test a) needs to be done in a lab (unless you happen to have a PCR machine at home..) and b) will take at least 4-6 hours, plus time to transport the sample to the lab and results out.
Your body makes antibodies against viruses and bacteria when you’re infected to help fight against them. The ‘home testing kits’ that have been in the news recently are antibody or serological tests. This test isn’t looking for the virus - it’s looking for your antibodies against the virus. After the infection has gone some of your antibodies remain in the body forever, and can help you fight against a second infection. Antibody tests look for antibodies in blood samples - either the ones that don’t last long (positive = you recently got infected) or ones that last forever (positive = you’ve been infected before in your life). In this way, you can find out if you are currently infected or have previously been infected. Because antibodies can be detected without having to be amplified like the RNA, they can be detected very quickly (in as little as 10 minutes!) in a device that would look and work a lot like a pregnancy test.
These tests could massively improve our ability to model the spread of the virus as we could see if people with mild or no symptoms have been infected, help make quick decisions about patients in hospitals and inform whether people need to stay at home or can go to work.
Some research groups have developed these tests in the US and antibody tests have been used at a small scale to study transmission in Singapore. The main difficulty with antibody tests is that there is a lot of variability in how people respond to infection and how many antibodies they make. Therefore the tests have to be optimised to be sensitive enough to pick up low antibody levels without mistakenly giving positive results for infection - both being too sensitive or not sensitive enough could have lots of negative knock-on effects.
Despite the obvious benefits of the antibody test, the RNA-based tests are still the gold-standard and most accurate way of looking for infection. Antibody tests will have to be fully compared with RNA-based tests to check they are accurate and reliable before they will be available in the shops, but with the huge drive to get these home testing kits working, this could be soon!
