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Covid

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Original poster

Do LFTs not show a positive if you have symptoms

22 replies

Ohnoreally · 02/10/2021 17:54

Please can someone set me straight

Do LFTs actually NOT show covid if you have symptoms, as in they literally do not work and won't show it up as a positive case,...

Are you supposed to get a PCR because you have symptoms and you're supposed to get one for one of the 3 main symptoms?

I'm not entirely sure I'm being clear here but I am trying to work out if I've taken an LFT and have a shocking dry cough, would the LFT actually not show it if it was covid?

There's covid where I work so I have been taking the LFTs wondering why it's negative as it's more likely I have it than don't.

Don't worry I've not actually gone and done anything since the cough started so I wouldn't have been unwittingly spreading it, I just have been assuming the LFT would show it and now I've realised maybe I've messed up! Help!

I don't know how I don't know this by now I'm sorry.

OP posts:

rattlemehearties · 02/10/2021 17:55

Exactly the LFT is not as reliable if you have symptoms. It's for picking up on asymptomatic cases. Book a PCR test if you have symptoms

Rosegoldfan · 02/10/2021 17:58

My friend has covid and tests every day. It keeps showing up positive and she does have symptoms. Can show for 3 months.

They aren't as accurate by a margin as the PCRs though.

Original poster

Ohnoreally · 02/10/2021 17:58

Right thank you, I will do! I've wrongly assumed that a symptomatic case would show on an LFT and then I should verify with a PCR.

I'm not being totally ignorant here - I had a PCR because of a hospital procedure a week ago, which was negative and I had a cold at the time. But no cough.

Now I've got a cough and so I've been assuming that it was the same cold and therefore not covid. But since lots of people at work have got covid I'm wondering if two things have blended into one.

I'll get a proper PCR test.

OP posts:

Original poster

Ohnoreally · 02/10/2021 18:00

@Rosegoldfan

My friend has covid and tests every day. It keeps showing up positive and she does have symptoms. Can show for 3 months.

They aren't as accurate by a margin as the PCRs though.

This is what I thought - everyone I know who's had covid with symptoms it's shown up on an LFT.

I've had a negative PCR just over a week ago, and then daily negative LFTs since id found out it was at work. But now I'm wondering if I should get another PCR.

OP posts:

Waxonwaxoff0 · 02/10/2021 18:00

LFTs are just unreliable, period. They're supposed to be a way of picking up asymptomatic Covid that would otherwise go undetected. You're supposed to get a PCR if you have symptoms because they are more accurate, not because LFTs don't ever show positive in symptomatic people.

My LFTs showed negative the entire time I had Covid, including before my symptoms began (had a positive PCR the same day I had a negative LFT) and when I developed symptoms a few days later.

dementedpixie · 02/10/2021 18:00

LFT is more accurate at detecting a positive case if you have symptoms compared to when you don't have symptoms. They have a high false negative rate though so can't be relied upon to rule out covid if you do have symptoms. Think its about a 70% accuracy when you have symptoms and about 50% if you dont

Watapalava · 02/10/2021 18:06

They are not be as accurate but if you have enough covid to show symptoms then i'm pretty sure it'd show on a lft. That's not rocket science really. You must be shedding some virus to be sick so lft will be exposed to more load

Mummyme87 · 02/10/2021 18:06

LFTs are damage limitation, no where near as sensitive and so if symptoms should do a PCR as much more sensitive. But are good for just random checking as cheap and quick

Waxonwaxoff0 · 02/10/2021 18:07

@Watapalava

I never showed positive on LFT even after developing symptoms. I did 3 out of interest while isolating.

CloseYourEyesAndSee · 02/10/2021 18:08

Of course they work if you've got symptoms but they aren't as reliable, so if you have symptoms you should take a PCR as you're more likely to get a false negative with a LFT and keep spreading it.

SingingSands · 02/10/2021 18:09

I had a positive LFT with symptoms.

UnmentionedElephantDildo · 02/10/2021 18:12

LFTs have a Hugh false negative rate.

If you are testing people without symtoms, and in the group 10 have covid, but only 5 test positive, you still remove 5 probably infectious people from circulation. Which is 5 more than you would have done with no testing. And that's a benefit.

But if you test people with symptoms, and 10 people have it (and very likely all would be found be found with PCR), but LFT finds only 5, you are leaving 5 probably infectious people out and about, who should not be. That's a detriment

MotherOfKitten · 02/10/2021 18:15

Lfts are not as reliable or accurate as pcrs which is why you need to get a pcr if you have any symptoms.

Lfts are only suitable for doing the twice weekly tests on school kids, teachers etc with no symptoms as even if they only pick up 50% of cases in those groups, that's better than nothing.

Both my DC tested negative on an lft (we had some lying around) but positive on a pcr the same day.

MrsTophamHat · 02/10/2021 18:15

I've just taken a PCR for this reason. I've got a terrible cough but no temp and no change in taste/smell. All negative LFTs. There is a cold doing the rounds here though so I think it's that but wanted to be sure.

Veuvelily · 02/10/2021 18:20

My LFT showed positive the morning after my fever, and kept showing positive for 8 days, I was on holiday. I had mild symptoms. I tested negative in an LFT to come home, but positive on day 2 PCR!

GoldenOmber · 02/10/2021 18:24

LFTs work the same whether you have symptoms or not. But they don’t pick up as many cases as PCRs do, so if you have symptoms that could be covid you’re better off getting a PCR.

I think some people have heard “LFTs aren’t for people with symptoms” and understood it as “LFTs stop working if you have symptoms”, which isn’t the case.

Whattheflecker · 02/10/2021 18:27

PCRs are also crucial for tracking the virus as the samples are analysed. So even if you have a positive LFT you should always get a PCR. The UK has been world leading at tracking the virus and we'll be in a far better place in the future because of it.

QueenofLouisiana · 02/10/2021 18:32

DH and I tested LFT positive- I had vague Covid symptoms, DH had none. DS never tested positive on LFT but had mild symptoms.
PCR picked us all up as positive.

Original poster

Ohnoreally · 02/10/2021 18:49

@GoldenOmber

LFTs work the same whether you have symptoms or not. But they don’t pick up as many cases as PCRs do, so if you have symptoms that could be covid you’re better off getting a PCR.

I think some people have heard “LFTs aren’t for people with symptoms” and understood it as “LFTs stop working if you have symptoms”, which isn’t the case.

Ok this is what I understood it to be until I started questioning myself just now.

LFTs do work if you have symptoms but overall they're less reliable so you should get a PCR

OP posts:

Gherkingreen · 02/10/2021 18:55

DS had symptoms (headache, racing heart rate, nausea) and the LFT showed a very strong line indicating he was + for covid.
A PCR confirmed he was +.

On day 9 he tested again with a LFT and there was a barely visible line and only in certain light.

Autumngoldleaf · 02/10/2021 20:37

As unmentioned said

They are so flimsy but they are all we have really.
Dd had several negative then had stronger symptoms for pcr then out of interest dh did lat flow on her and it was very faintly negative.

TheVolturi · 02/10/2021 20:49

I had covid two weeks ago and tested before symptoms and while I had symptoms. Really strong positives every time. In fact it actually took 11 days for me to get a negative!

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