Lateral Flow Tests

[mothman]

I think you made the right decision. I know it fucking sucks, especially when the cunts in charge of this whole shitshow feel these rules don't apply to us.

[Fambo Number Mive]

Hope your PCR test is negative, wooders 1978

[jobotic]

I'm missing something here

https://www.theguardian.com/world/2021/dec/13/can-you-trust-a-negative-lateral-flow-covid-test

How does this

You wake up with a pounding head, sore throat and runny nose: you reach for one of those lateral flow tests (LFT) you've got stashed away, just to check it is not Covid. If it returns a single red line (negative), then most people will pop a couple of paracetamol and go about business as normal – particularly if you've been double-jabbed. It probably is just a cold, after all.

Yet, the emergence of Omicron has thrown a spanner in the works. According to the latest data, just one month after your second Pfizer or AstraZeneca jab, the ability of antibodies to neutralise Omicron is 30 times lower than if you were infected with the Delta variant – reinforcing the message that double-vaccination is no guarantee against infection.

The study follows recent UK Health Security Agency (UKHSA) data, suggesting those who have been double-jabbed with the AstraZeneca vaccine have about 10% protection against symptomatic infection with Omicron six months after their second jab, compared with 40% protection against the Delta variant.

mean this?

So, if you're relying on a LFT to guide whether or not it is safe for you to leave the house, the odds of it being wrong just got higher.

[Huxleys Babkins]

I'm old enough to remember when lateral flow tests were supposed to only be used if you had no symptoms.

[greencalx]

I'm missing something here

https://www.theguardian.com/world/2021/dec/13/can-you-trust-a-negative-lateral-flow-covid-test

How does this

mean this?

I think they just mean that if LFTs are less sensitive to ο than δ, and ο is becoming more prevalent then the probability of a false negative goes up. But they might not mean that, because very few journalists have any statistical/mathematical understanding, and it's one of the many reasons why they are best ignored.

[Zetetic]

I think the point is actually very little to do with lateral flow tests themselves.

The point is that omicron has changed the probabilities of CoViD-like symptoms (and indeed some non-traditionally-CoViD-like symptoms...) being a good indicator, amongst the un-boosted-but-vaccinated, that you have CoViD.

The emergence of omicron means that 1) such people can more easily be (re-)infected with CoViD, and 2) such symptoms are now more likely to be the product of CoViD.

The sensitivity of LFTs might be the same for different variants of CoViD, but if incidence is rising (due to a particular variant) then the false negative rate will rise.

[MojoJojo]

I don't think they are saying that, although they are implying it - if there was any evidence LFTs were less effective at detecting Omicron it would be massive news. I think that they are saying is that if more people have covid, then a negative LFT is more likely to be false negative. This is a truism of testing - to take it to the extreme, if no one had covid the possibility of a false negative is zero - but it's not particularly interesting and they haven't explained themselves.

(edit - what Z is saying)

[jobotic]

Thank you. I understand now.

I use an LFT every couple of days when asymptomatic because I work with the public and have kids at school (and occasionally go out) and if I have it I want to know so I don't spread it. I know they're far from perfect but what else are you gonna do? So they're no more or less reliable for that.

[Zetetic]

but it's not particularly interesting

I think it is a bit because a lot of us - and I include myself in this - have probably had symptoms of a respiratory virus in the last few months and (via LFTs and PCRs and disease course) convinced ourselves it's something boring (Rhinovirus, RSV-in-an-adult), and most of us were probably right.

But the complancency that can engender - and again I include myself in this - probably needs to change rapidly ... this week? PlausiblesSymptoms-plus-negative-LFT probably should be leading, again, to a decent degree of isolation.

It's a shame that the piece isn't very strong.

[flotemysost]

Another isolation quandary here: so, my flatmate woke up this morning with mild symptoms (new continuous cough) and went to get a PCR today. We've both taken a couple of lateral flows each today (all negative) so I'm hoping the PCR will follow suit.

However the advice re: isolating on the NHS page isn't completely clear:

When you do not need to self-isolate

If you live with or have been in contact with someone with COVID-19, you will not need to self-isolate if any of the following apply:

you're fully vaccinated – this means 14 days have passed since your final dose of a COVID-19 vaccine given by the NHS
you're under 18 years, 6 months old
you're taking part or have taken part in a COVID-19 vaccine trial
you're not able to get vaccinated for medical reasons

However, if you live with or have been in contact with someone who may have the Omicron variant of COVID-19, this does not apply and you'll still need to self-isolate. NHS Test and Trace will contact you if this is the case.

Even if you do not have symptoms, you should still:

get a PCR test on GOV.UK to check if you have COVID-19
follow advice on how to avoid catching and spreading COVID-19
consider limiting contact with people who are at higher risk from COVID-19

The bolded bits are what's confusing me - I'm double-jabbed, so don't need to isolate according to the first bit, but given how things are, if flatmate does have it then there is a good chance it's the Big O - so according to the second bolded bit, I would need to isolate after all. I mean, if flatmate's PCR comes back positive then it would make sense for me to also get a PCR, but if mine is negative, then I don't know - would I still need to isolate after that? Or is that when the daily LFTs for seven days kicks in? (It doesn't seem to mention that bit on the website but everyone's saying them's the rules now.)

I feel fit as a fiddle btw, no symptoms at the moment. Flatmate is already boosted, I'm due to get mine tomorrow, as long as I don't get shot-blocked. Hoping it's just standard festive lurgy, but you never know.

[mothman]

I feel utterly rubbish. Tired, achey, washed out, occasionally like I'm short of breath although like I'm not, that tingling feeling you get in the nose and throat and face and teeth like I'm coming down with a cold, very occasional sharp pain behind my left eye.

The UK government has always stressed that people with Covid symptoms should seek a PCR test, rather than relying on a LFT. Yet, it still defines these symptoms as a high temperature, new, continuous cough and/or a loss or change to your sense of smell or taste – despite widespread evidence that headaches, fatigue, a sore throat or runny nose are also common Covid symptoms.

Temperature normal, sense of taste & smell fine, no cough. Two LFTs both negative. Dead soon?

[flotemysost]

I took a PCR last year when likewise I had none of the official symptoms but for a couple of days was freezing cold, shivering like a nervous whippet and generally feeling like I was moving around underwater (it was negative) - but, I appreciate it's easy for me to go "just get a PCR!" as a child-free person who can work from home (also, that was before LFTs were widely available). Sorry to hear you're not well anyway, hope you feel better soon.

I also had the sharp pain behind the eye thing at the start of this year, weirdly - like a headache that was concentrated behind the eye, and dizziness. I took another PCR days after having that - negative, though it's possible I'd missed the window for an accurate result (because I kept thinking "ah it's not an official symptom, it's probably fine"). But then there are so many things that can cause headaches and eye strain, so who knows.

Sorry, this isn't a very helpful post is it.

[mothman]

No, but thank you for listening and responding. ;-)

I may just be run down. My 4-5hr-a-night sleep regimen finally doing me in. I've also been stress eating and have put on weight.

[wooders1978]

No, but thank you for listening and responding. ;-)

I may just be run down. My 4-5hr-a-night sleep regimen finally doing me in. I've also been stress eating and have put on weight.

I feel kinda the same so maybe we'll be bedmates in the ozzy
Hopefully get my pcr back today

[mothman]

Fingers crossed for you!

[flotemysost]

PCR confirmed my flatmate def has some form of it, only mild symptoms thankfully (we're communicating by text only at the moment, so we haven't actually been in the same room since symptoms started). Apparently the current guidance for vaccinated, symptom-free household members is daily LFTs, unless it turns out to be Crazy Cron in which case I'd also need to isolate and get a PCR (not sure how long the genetic sequencing takes - a few days after the initial PCR result? Are they even checking every test for it?). I'm still a bit confused tbh.

I guess I'm lucky that a) I can work from home anyway and b) it's not like I share a room/bed with the person who's isolating - thankfully the layout of the flat makes it pretty straightforward to ensure our paths don't cross for a while - but I don't imagine it's very helpful advice for people who don't have those options.

Will probably hold off from pissing in the shower and licking everyone else's butter for a few days as a precaution, anyway.

[steveh]

In case it helps anybody, there are anecdotal reports that with Omicron throat swabs may give a positive result earlier than nose swabs do.

[MojoJojo]

Please don't repeat anecdotal reports like that. It just adds to the whirlwind of misinformation that leads to increased anxiety in some and risky behaviour in others.

[mothman]

I'd have to agree. There are anecdotal reports that the vaccines improve your 5G reception, after all. 🙄

[Crenners]

steveh has posted a wealth of accurate, moderate information in this thread, far beyond anyone else.

[steveh]

I can't find the reference to it now, but there was research reported last week about Omicron taking slightly longer to appear in mucus due to its different infection mechanism / target so may not be without scientific merit. However, I take the point about anecdotal reports.

[olliebean]

I saw a tweet or something where someone had done a few Lateral Flow tests over the course of a day - the sort you're only supposed to put up your nose - and wiped half of them against his tonsils (without doing the nose), and it clearly showed the red line indicating a positive test appearing earlier in the day on the tonsil tests than the nasal ones.

[Uncle TechTip]

Red line was control I thought, faint black line for positive test.

[Ferris]

I had a spare one and took while isolating to check I was doing it right (2cm up nose, give it 5 goes round then next nostril and into the little tube thing).

Was very prominently positive so they absolutely work on omicron for whatever that's worth

[MojoJojo]

I saw a tweet or something where someone had done a few Lateral Flow tests over the course of a day - the sort you're only supposed to put up your nose - and wiped half of them against his tonsils (without doing the nose), and it clearly showed the red line indicating a positive test appearing earlier in the day on the tonsil tests than the nasal ones.

Apart from the sample size, that doesn't say anything about omicron.

[C_Larence]

I had a spare one and took while isolating to check I was doing it right (2cm up nose, give it 5 goes round then next nostril and into the little tube thing).

Was very prominently positive so they absolutely work on omicron for whatever that's worth

How do you know you had Omicron? My PCR was positive but had no mention of variants.

[Ferris]

No other variant where I live. Omicron or nothing, baby!

[olliebean]

Red line was control I thought, faint black line for positive test.

Is it? Perhaps I'm misremembering. I haven't done one in a while.

(Checks booklet) The little diagram shows both lines as red, and the text describes them both as coloured lines.

[C_Larence]

Both lines on my LFTs have always been red, although I've seen pictures online of black lined tests, perhaps those are the antigen ones? Or is that what an LFT is?

[olliebean]

LFT is an antigen test. (I have no specialised knowledge of this, it just says so on the box.) There may have been different sorts of LFTs - the current ones require swabbing of nostrils only, whereas earlier they required tonsils and one nostril, like the PCR tests. A quick Google image search shows positive tests with both red and black lines. In general, it looks like the ones with QR codes on them have a black line, and the ones without have red.