In an April 5th memo, Professor Sir John Bell noting that no tests to date have performed well. The UK government testing strategy is intended to manage all aspects of Covid-19, including PCR tests on swabs from the nose or throat to detect the virus as well blood testing to detect people who might have had the virus and hence be protected with immunity. These people would be able to go back to work without the fear of being infected again because they are now immune tothe disease. This combination provides citizens the information they and the health system need to manage those with the disease by giving access to rapid disease diagnosis and manage the population as a whole to ensure we will not put ourselves or others at risk while the virus is circulating. Large scale testing will be crucial for getting us back to our normal lives in the coming months. One strand of the government strategy has been to use home testing kits to allow people to test and see whether they have long term immunity and hence can confidently go back to work. Creating home test kits is, however, not easy. They detect antibodies in blood by capturing these antibodies on virus components held in the test kit. Blood flows from one end to the other, the anti virus antibodies are captured and a signal appears as a line on the test device. This can be read by the person at home or on their mobile phone camera. If there are no antibodies no line appears. There are many challenges to creating accurate tests; hence these tests need to be validated carefully. There are 100 or more such tests kits from different suppliers available for identifying Covid-19 antibodies. Crucially it is essential that the test does not tell you are positive for anti-Covid serology when you are not; otherwise you might return to work when you are not immune. Similarly, it is important that the test does not tell you that you are not immune when you actually are. To validate these tests you need to obtain a range of tools:
- You need a gold standard test so you know the correct answer and you need sera from patients who have recovered from the virus infection they had approximately 28 days before.
- You also need blood from people who donated before the epidemic so you know whether you falsely see positive tests when there is no Covid-19 in the sample.