Why do lateral flows give a false reading with symptoms?

[Burritobowl84]

www.google.co.uk/amp/s/www.express.co.uk/life-style/health/1533126/coronavirus-omicron-variant-lateral-flow-test-symptoms-false-reading/amp

I’ve read a few articles like this online, and they all say lateral flow tests ‘will’ (not ‘may’) give you a false results if you have symptoms. But no further information on what the reason is for this? Can anyone explain? Has anyone come across any info stating the reason as to why this is the case?

No idea but I tested positive on 2 laterals but negative on a pcr. Had to go to work (customer facing retail job) had no symptoms though.

Wow @Pickledlipstick

I wonder if that policy also applies to people who work in bars and restaurants where customers wouldn’t be allowed in if they had a positive lateral flow? Or is that just a policy for essential retail workers maybe?

I had symptoms and tested positive on a lateral flow (confirmed later with a positive PCR).

The BMJ also say that lateral flow tests are better at identifying people with symptoms. I'd rather trust the BMJ than a doctor appearing on This Morning.

www.bmj.com/content/372/bmj.n823

In brief, the difference with lateral flows are more of a snapshot that seem to show positive when someone is infectious with Covid whereas PCR shows positive for signs of Covid but not necessarily infectious at the time of the test.

It's not that they give false results, it's that they're just not that reliable.

If you have no symptoms AND test negative, there's far more chance that the negative is correct than if you have symptoms. LFTs are really meant for picking up asymptomatic cases. If you have symptoms, you really need a PCR as they are much more reliable.

That's simply untrue.

LFTs are a quick and simple way of reducing the number of people walking around with Covid by picking up a large number of people with asymptomatic Covid, (and also people who have cold-like symptoms who might not bother with a PCR though that's not official advice).

The reason they're not advised if you have symptoms is simply because they're not as reliable as PCRs.

They are actually more reliable if you do have symptoms but as they have a high false negative rate a negative test when you have got symptoms can't be relied upon to be a true result.

Lft have been extremely effective among families and cases I know at school.

One Gp friend only knew she had it (cold) due to lft and then they accurately picked up each member of her family of 5 over the next 3 weeks as they came down with it one by one.

The rules have always been to get a pcr with symptoms.

The problem is that for some symptoms are now a mild cold. No loss of taste etc. And there's hinder of colds flying around.

If I had headache, cough and loss of taste/ smell I'd definitely get a pcr.

They're completely different tests too. The whole point is to do them twice a week or more as a "net" to catch sneaky infections.

They're not proof of infection without pcr.

Though there's been a few cases of repeated positive lft with symptoms and neg pcr, in which case you err on side of caution, isolate and re test pcr

@megustalacerveza

It's not that they give false results, it's that they're just not that reliable.

If you have no symptoms AND test negative, there's far more chance that the negative is correct than if you have symptoms. LFTs are really meant for picking up asymptomatic cases. If you have symptoms, you really need a PCR as they are much more reliable.

PCRs aren't necessarily more reliable as I found out earlier this morning and prompted me to start a thread! 30% false negative!

www.bmj.com/content/372/bmj.n287/rr

@megustalacerveza

It's not that they give false results, it's that they're just not that reliable.

If you have no symptoms AND test negative, there's far more chance that the negative is correct than if you have symptoms. LFTs are really meant for picking up asymptomatic cases. If you have symptoms, you really need a PCR as they are much more reliable.

PCRs aren't necessarily more reliable as I found out earlier this morning and prompted me to start a thread! 30% false negative!

www.bmj.com/content/372/bmj.n287/rr

@megustalacerveza

It's not that they give false results, it's that they're just not that reliable.

If you have no symptoms AND test negative, there's far more chance that the negative is correct than if you have symptoms. LFTs are really meant for picking up asymptomatic cases. If you have symptoms, you really need a PCR as they are much more reliable.

PCRs aren't necessarily more reliable as I found out earlier this morning and prompted me to start a thread! 30% false negative!

www.bmj.com/content/372/bmj.n287/rr

Apologies, I didn't mean to spam this thread... Was told messages had failed when they clearly hadn't!

@IdrisElbow

Everyone I know who has had covid recently, and that's quite a lot of people, have had a positive LFT prior to a positive PCR test. They only took the LFT because they were showing some kind of symptom (though not necessarily the 3 main ones). So the reliability of the LFTs anecdotally seems to be quite high.

They are more reliable if you have symptoms and less reliable when you don't.

@WarriorN

Lft have been extremely effective among families and cases I know at school.

One Gp friend only knew she had it (cold) due to lft and then they accurately picked up each member of her family of 5 over the next 3 weeks as they came down with it one by one.

That's confirmation bias. There will be plenty of other families who never knew they were all infected because their LFTs showed negative the entire time.