黑瓜吃料网

Dr Alexander Edwards, Associate Professor of Biomedical technology at the 黑瓜吃料网 has answered questions about the use of lateral flow tests as part of the UK鈥檚 lifting of lockdown measures during the Covid-19 pandemic.

How easy is it for students and their parents to do these tests at home?

鈥淎 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 it鈥檚 a new thing to do.

鈥淲e 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.鈥�

How can someone make sure that the tests are as accurate as possible? What鈥檚 the best practice? 

鈥淭he best tip is not to rush the first few times. Doing the test doesn鈥檛 take long once you get used to it. But do take your time looking through the instructions and getting ready before you start.

鈥淐learing a little space on a table or desk just for testing helps a lot- maybe use a tray or keep everything in a 鈥榯esting box鈥�. Finally: do use a timer! Don鈥檛 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?

鈥淓ven 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 don鈥檛 follow those exact kit instructions, or if you modify them (e.g. reading the test result at a different time), it鈥檚 possible to get test failure or even to interpret the result wrong.

鈥淭he 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? 

鈥淚t鈥檚 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 鈥� because they lack the complex bioanalytical steps used in labs that can detect even a few molecules of virus.

鈥淭here is also no doubt that lateral flow rapid tests are simpler, cheaper and more portable.鈥�

Find out more about Dr Alexander Edwards' research about improving instructions for testing

How reliable and accurate are Lateral Flow Tests?

鈥淥ne of the most frequently discussed features of rapid lateral flow tests is accuracy. However, it鈥檚 really important to recognise that the focus on accuracy is a distraction from the real question for any diagnostic testing program: is it useful?

鈥淰ery 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 can鈥檛 access. Furthermore, 鈥渙fficial鈥� accuracy measured in highly regulated ways, does not directly predict usefulness.

鈥淭here is so much detail 鈥� terms like sensitivity, specificity, positive or negative predictive value, false positive or false negative 鈥� and the detail does matter. We have plenty of data already, yet don鈥檛 have all the answers but we are faced with an urgent need to act.

鈥淐ompromises 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.鈥�

Is there a risk of false reassurance from false negatives?

鈥淲e 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 doesn鈥檛 鈥減rove鈥� 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 鈥� even for lab PCR testing of symptomatic patients 鈥� that negative results cannot rule out COVID-19.

鈥淔or 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.

鈥淭he 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 鈥榡ust work鈥�.鈥�

How about the other way round? Could students be missing school because of false positives?

鈥淭his is not so much of a concern for two reasons.

鈥淔irst, 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 don鈥檛 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.

鈥淪econd, 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.鈥�

鈥淭he 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.鈥�

What will happen if some students are refusing to take them? Doesn鈥檛 it undermine the whole strategy?

鈥淭he 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 don鈥檛 believe mandatory testing is necessary or helpful.

Will it have much of an impact on the pandemic?

鈥淚t鈥檚 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.

鈥淭he 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 won鈥檛 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.鈥�

How does community testing link to the vaccine program and re-opening from lockdown?

鈥淭he virus won鈥檛 just 鈥榞o away鈥�. 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."