Lateral Flow Tests vs PCR?

[coffeepleeease]

Can someone please explain to me why you can’t take a lateral flow test if you have symptoms? Won’t it still pick up a positive? How would it pick up a positive in an asymptomatic person, but not in a person with symptoms? I’ve heard that lateral flow tests aren’t as reliable, but if that’s the case then what’s the point in taking them regularly if your asymptomatic? I’m just a bit confused really, not for one minute suggesting I wouldn’t follow the rules, just don’t understand!

Lateral flow tests are only really good for preventing silent spread at a population level - they do miss cases, but the idea is that so many people use them so regularly that this catches the majority of asymptomatic cases and on the whole works, as long as most people are doing it. It isn’t a medical diagnostic- the PCR tests are needed for this. They are hugely more expensive, but hugely more accurate, so will give an individual a diagnosis. Because they take longer to turn around and require a lab and trained people to run them, they really aren’t suitable to population monitoring.

Also because the PCR tests are processed by a lab, they can be used to find out which variant of the virus the person has. This is not possible with home testing.

If you have 20,000,000 people who could pick up covid at any moment, and you want to reduce the number spreading virus to others, you want to identify as many as possible, as soon as possible.

20 million PCR tests REGULARLY isn't possible.

20 million LF tests IS possible. If they only pull out 40% of infected people who have no reason to suspect they have covid, that's a LOT fewer people spreading the virus.

However, far fewer people have symptoms- it IS possible to test these with PCRs and there is a much higher likelihood they have covid. Using PCR anyone with covid WILL be identified. But using LF tests, only ~50% would, meaning 50% would continue to circulate believing they were virus free.

PCR is more sensitive than LFT.

If you're showing symptoms then a PCR is more reliable and can be assessed properly in a lab allowing any variations to be recorded.

Whilst LFT tests are mostly accurate when taken properly user error can result in a false negative meaning that people wouldn't always isolate/report.

LFT’s are basically embodiment of not letting perfect getting in the way of the good. No they aren’t 100% reliable but if they can pick up an asymptomatic infection that otherwise wouldn’t have been identified there’s the potential to break a chain of infection.

I had read that initially they were designed to pick up symptomatic cases and are better at doing that. Totally agree with everyone above - and obviously symptomatic cases should get a PCR, but I think statistically they are better at picking up symptomatic people.

Thanks for all the replies!

@loweylo I think that might lead us back to the argument about pre-symptomatic and what counts as asymptomatic. By that I mean there have been a great deal of people who haven’t displayed the three official symptoms and have presented atypically (within the definition of current U.K. official covid symptom guidelines)with things like a mild sore throat, headache, fatigue etc.

I don’t think there’s any monitoring of whether LFT positives are experiencing any symptoms at all so it may be that what we class as asymptomatic infections have actually caused other symptoms that would have otherwise gone untested.

Compared to other countries we have a very short list of symptoms to trigger a PCR test.

It was this article that I read if anyone’s interested. They’re still pretty inaccurate, but it’s quite an interesting read www.bmj.com/content/372/bmj.n823

@Cornettoninja It’s so true about all the different symptoms and our limited list. I think we must have missed a lot of cases because of that. Kids in particular as most of them don’t seem to get a cough (according to that Zoe app). It’s certainly an odd disease .