What is the point of Lateral Flow

[Blondie107]

I have heard that many employers are sending people to have Lateral Flow Tests every week or so. However doing more research I've learned that they have a 50% accuracy when done at home and not that much more when done at LFT centres. False positives are rare but there are lots of false negatives that mean the test has been unable to detect the virus

And then if it comes up positive you have to book a PCR straight away to "confirm" it which surely means that they know they're not reliable?

Your points are all valid, but LFTs detect some cases that would otherwise have gone undetected, leading to further spread.

The concern with them is that people think a Negative result means they definitely haven't got Covid and visit granny or whatever.

It’s to catch asymptomatic cases. Yes, they won’t catch them all but they will catch some. & some is better than nothing. If it catches 50% of the asymptomatic cases in a school then that’s helpful. Obviously be more helpful it caught 100% but they don’t. But that doesn’t mean they aren’t helpful.

They're not great but they're better than nothing. And have the huge advantage that results are available so quickly.

I guess if you have 20 people, and 4 of them are asymptomatic but positive, if they all are taking lateral flow tests, in theory 2 of those 4 positives would be picked up, then confirmed with the more reliable tests. Meaning 2 less people spreading it around unknowingly.

It's unrealistic to use the more accurate one as a way of regular testing, because of how long it takes to process them. So I guess this is a way of catching SOME asymptomatic cases, even if not all. And catching some is better than catching none.

I wondered this. If someone's LFT is positive what happens? And what does that mean for their colleagues?

I'm aware that they aren't particularly accurate, but as you have said, false positives are pretty rare, it's false negatives that are the problem.

The way I see it, even if they only pick up 50% of asymptomatic cases, that's still significant. Surely it's better to catch 50% rather than none at all?

DD has been doing them in school and we have been doing them at home. The school has reported that two asymptomatic cases (subsequently confirmed by positive pcr tests) have been picked up by the LFTs since they reopened earlier this month. The kids in question were able to isolate, as were their close contacts. That wouldn't have happened if they hadn't done the LFTs, so presumably those two kids would have remained in school spreading the virus.

Surely it's better that we pick up what we can, even if it isn't 100%?

The kids in question were able to isolate, as were their close contacts. That wouldn't have happened if they hadn't done the LFTs, so presumably those two kids would have remained in school spreading the virus

I would assume they were spreading the virus already? That's what I don't understand. Why a positive result doesn't affect everyone in the way it would if you had the useless app and being in contact meant you had to isolate etc...

I think they do more harm than good. My daughter is a nurse and uses the lateral flow tests twice a week. The results showed her as being negative when she first developed symptoms. She eventually booked an actual test once her symptoms were more obvious. Her test came back positive and when she did a lateral flow test, just out of curiosity, it still showed as negative. She said colleagues put off getting tests if their lateral flow tests are negative, even if they have symptoms. I think they're useless at best and counter productive at worst.

All the secondary kids had to test before they went back to school on 8th March, so the asymptomatic cases weren't spreading it around school.

I would assume they were spreading the virus already? That's what I don't understand. Why a positive result doesn't affect everyone in the way it would if you had the useless app and being in contact meant you had to isolate etc...

How do you mean? Sorry, might be being thick but I don't understand.

At our school, the close contacts of positive tests have been isolating. Is this not what is happening elsewhere?

And yes, of course it's likely that the kids may have been spreading the virus before they test positive, but by testing twice a week, I guess they catch it at a relatively early stage and hopefully reduce the overall number of people that they're likely to spread it to?

My daughters school didn’t. They tested on their first day back (where the whole year group were held in the hall) and then the subsequent tests were down during the normal school day...

Done during

@AlexaShutUp

I would assume they were spreading the virus already? That's what I don't understand. Why a positive result doesn't affect everyone in the way it would if you had the useless app and being in contact meant you had to isolate etc...

How do you mean? Sorry, might be being thick but I don't understand.

At our school, the close contacts of positive tests have been isolating. Is this not what is happening elsewhere?

And yes, of course it's likely that the kids may have been spreading the virus before they test positive, but by testing twice a week, I guess they catch it at a relatively early stage and hopefully reduce the overall number of people that they're likely to spread it to?

I think it might be me that's being thick I'm not too sure. I mean that they had the positive LFT so they had Covid at that point so had potentially already given it to the rest of the building.

I don't have any school age children so I am out of the loop there I was thinking more about workplaces.

I'm not sure what the point of a confirmation test is, when (as I understand) fse positives are vanishingly rare, as they should be.

I don't think they've even spelt out what you do if your confirmation test is negative

@GreenBalaclava

All the secondary kids had to test before they went back to school on 8th March, so the asymptomatic cases weren't spreading it around school.

That sounds more sensible.

They’re not great but it’s better than nothing. At my workplace we have 2 PCRs each week and 1-2 LFT on top. I think that’s the safest way to go, but PCRs are expensive.

What I find annoying is that you do them and report them but can then lie. Why can't they develop a scan that detects the result?

@DurhamDurham

I think they do more harm than good. My daughter is a nurse and uses the lateral flow tests twice a week. The results showed her as being negative when she first developed symptoms. She eventually booked an actual test once her symptoms were more obvious. Her test came back positive and when she did a lateral flow test, just out of curiosity, it still showed as negative. She said colleagues put off getting tests if their lateral flow tests are negative, even if they have symptoms. I think they're useless at best and counter productive at worst.

That's not the fault of the test. How do nurses not know that they should get a PCR test with symptoms?

That's a really worrying lack of knowledge from medical staff, no wonder there are so many infections linked to hospitals.

I think it might be me that's being thick I'm not too sure. I mean that they had the positive LFT so they had Covid at that point so had potentially already given it to the rest of the building.

OK, I get what you mean, and yes, I guess it is a risk, but if my dd went to school with an asymptomatic case on Monday, I guess she might come into contact with, say, 40 people. She might well spread it to some of those people (who may then spread it to others, so yes, there is a risk.

But then if she went into school on Tuesday, she might come into contact with a further 25 people, some of whom would be infected. So that would result in more people spreading the virus overall?

Whereas, if she isolated on Tuesday because of a positive test, those extra 25 people would not be exposed. And the close contacts that she infected on Tuesday would also be isolating and therefore spreading it to fewer people as well.

So, as I see it, the LFTs won't actually stop the virus from spreading, but they will hopefully slow down the exponential growth that would occur if kids were spreading it around asymptomatically without any checks in place?

@Sparklingbrook

I wondered this. If someone's LFT is positive what happens? And what does that mean for their colleagues?

They get sent for a PCR test and isolate until results come back.

Nothing happens to their colleagues as a result of LFT. If the colleagues are also LFTing and social distancing there’s minimal risk.

@purplebatbear

What I find annoying is that you do them and report them but can then lie. Why can't they develop a scan that detects the result?

But how would they know the person who did the test is the ones you're reporting? They'rebintended to rely on honesty, other than administering by a hcp which would be expensive. I don't see that there's any other option.

Thanks @TomHardyAndMe. If this ever gets introduced at my work I won't be rushing I don't think.

@StealthPolarBear That's the issue. Relying on honesty when quite often people just aren't honest. I work in a school and we've had parents reporting negative lateral flows when it has transpired they were probably positive due to us having to send home their children due to symptoms. It's a joke. The system should expect photographs which then show the test ID number, which should be linked to one specific person. However, you're right - anyone could actually take the test and pretend it's someone else's. It's all just such a useless mess.

They pick up a decent proportion of asymptomatic and pre symptomatic cases, reducing the spread from those cases. They’re not perfect and won’t pick up all cases, but it all helps.