10 March 2021
Dr Alexander Edwards, Associate Professor of Biomedical technology at the University of Reading has answered questions about the use of lateral flow tests as part of the UKâs lifting of lockdown measures during the Covid-19 pandemic.
How easy is it for students and their parents to do these tests at home?
âA lot of work has been put into making home testing as simple, safe and effective as possible. It might not feel easy first time, simply because itâs a new thing to do.
âWe already follow instructions at home- for example cooking a new recipe or even re-heating ready meals. Regular home testing is straightforward once you get the hang of it.â
How can someone make sure that the tests are as accurate as possible? Whatâs the best practice?
âThe best tip is not to rush the first few times. Doing the test doesnât take long once you get used to it. But do take your time looking through the instructions and getting ready before you start.
âClearing a little space on a table or desk just for testing helps a lot- maybe use a tray or keep everything in a âtesting boxâ. Finally: do use a timer! Donât just guess the time: get the timer set up before you get started, either on your phone or dig out a timer from the kitchen.
What are some of the most important things to watch out for when doing one of these tests?
âEven though they all work the same way, there can be differences between different lateral flow test devices and the home testing kits, so it is vital to follow the specific instructions in your kit. If you donât follow those exact kit instructions, or if you modify them (e.g. reading the test result at a different time), itâs possible to get test failure or even to interpret the result wrong.
âThe good news is the actual steps are pretty simple, so if you just follow those instructions step-by-step, you can be confident you did it right.
How do Lateral Flow Tests compare with laboratory PCR tests?
âItâs a simple trade off of speed and ease versus accuracy. There is no doubt that lateral flow rapid tests are less sensitive than laboratory tests â because they lack the complex bioanalytical steps used in labs that can detect even a few molecules of virus.
âThere is also no doubt that lateral flow rapid tests are simpler, cheaper and more portable.â
Find out more about Dr Alexander Edwards' research about improving instructions for testing
How reliable and accurate are Lateral Flow Tests?
âOne of the most frequently discussed features of rapid lateral flow tests is accuracy. However, itâs really important to recognise that the focus on accuracy is a distraction from the real question for any diagnostic testing program: is it useful?
âVery few tests are perfect. But they remain one of the most powerful tools for modern medicine. A less accurate test that you can use is better than a perfect test you canât access. Furthermore, âofficialâ accuracy measured in highly regulated ways, does not directly predict usefulness.
âThere is so much detail â terms like sensitivity, specificity, positive or negative predictive value, false positive or false negative â and the detail does matter. We have plenty of data already, yet donât have all the answers but we are faced with an urgent need to act.
âCompromises are essential. With lateral flow, the compromise is between reduced accuracy vs easier to access. We must make every effort to make lateral flow tests as reliable as possible. But there are plenty of reasons to expect that frequent testing even with less sensitive tests can be very effective.â
Is there a risk of false reassurance from false negatives?
âWe do know the rate of false negatives is significant, and this is important for everyone to understand. The messages from public health officials continues to be clear, that even if you test negative with a COVID-19 test, it still doesnât âproveâ that you are safe and not infected. This is especially true with regular asymptomatic testing using lateral flow rapid tests. But it has always been true â even for lab PCR testing of symptomatic patients â that negative results cannot rule out COVID-19.
âFor example, you could test negative but then become positive the next day, just because you are starting to get ill, as the virus can grow quickly once it takes hold in the body. Because lateral flow rapid tests can only detect the higher levels of virus, you could have a low level infection and be negative, but quickly become infectious.
âThe further uncertainty is that lateral flow testing appears to have different rate of false negatives depending on who does the testing. We must continue to work on this. It may simply be that people need some practice to operate these tests, but once they get the hang of the process, they become more reliable. Home and community testing is still very new, so we must work hard to make it as easy and effective as possible, and not assume it will âjust workâ.â
How about the other way round? Could students be missing school because of false positives?
âThis is not so much of a concern for two reasons.
âFirst, the false positive rate seems to be extremely low for lateral flow rapid tests. We expect it will affect less than 1 in 300 people, and this could be even lower as some studies hint that the false positive rate could be 1 in 1000 or lower. As the levels of infection fall, the number of people with false positive results will still represent a big proportion of anyone testing positive. But we donât expect false positives to lead to whole schools being regularly closed. We still need more data on the exact numbers of false positives, but it seems very likely that most schools will find more student absences due to normal illness, than from false positives.
âSecond, we have to work to minimise any harm from false positives, and to remember how harmful uncontrolled spread of COVID-19 is to the whole community. Support for people to self-isolate remains vital. But I hope individuals affected can understand it is far better for them to spend a few days studying at home, than to risk the whole class becoming infected because of further spread. Or for the whole country to have to return to national restrictions and close schools again.â
âThe program must be carefully monitored to check for excessive false positives, but it should be far better to have most pupils in school with a few students isolating due to false positives, than having everyone home schooling because there is no other way to avoid spread.â
What will happen if some students are refusing to take them? Doesnât it undermine the whole strategy?
âThe more people who join the testing program, the more likely it is to identify cases early, supress virus spread and prevent larger outbreaks. But I donât believe mandatory testing is necessary or helpful.
Will it have much of an impact on the pandemic?
âItâs simple: either everyone has to stop having contact with other people, or only those people who are infected at any one time avoid contacts. The only way to identify infected individuals is through testing.
âThe aim of community testing is to speed up detection of cases as early as possible, and thereby improve test-trace-isolate public health measures that restrict spread. Testing alone wonât help, but combining regular testing with other public health measures can slow spread so that case numbers fall (rather than rise). Without community testing the virus can spread undetectably before anyone experiences symptoms. By the time someone develops a cough/fever/loss of taste/smell, books a test, has the test, and receives the results, it may be several days later; during this time, the virus may have travelled silently, infecting many more people.â
How does community testing link to the vaccine program and re-opening from lockdown?
âThe virus wonât just âgo awayâ. We must prevent spread, otherwise yet again we will see rapid growth again that will rise to the high numbers of infections that we know will shut everything down. The vaccination program brings massive benefits, but it will still be a while before everyone (both in UK and globally) has protective immunity; until that point this virus is dangerous and every tool to reduce spread is valuable."
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