How likely that 4 LFT’s could be wrong?

[bellsoflemon]

I do twice weekly LFTS’s Wednesday and Sunday.
I tested negative Wednesday.

As part of work I went to a lab on Thursday who required an LFT to be taken, which was negative.

Today i started with an awful cold, sore throat and feeling generally a bit run down.

I’m at a family bbq tomorrow so I did an LFT this morning which was negative, another one this evening which was also negative.

Have messaged in my family group to say I’m thinking of not going to BBQ and they’ve all told me the tests are negative and to still go.

I started with a sore throat Tuesday. Cough Wednesday. Lost my sense of smell Thursday. Booked a test for Friday and had results today.

Negative.

I would still get a PCR test to be sure as those are what you take for symptoms not a lateral flow test.

@BowtieBling

My understanding is that LFT is useless if you display symptoms. No symptoms, lateral flow test. Symptoms, PCR test.

That was my understanding too.

I’d not go to a social gathering with a cold or other bug anyway as it’s not fair to spread germs round.

I dont understand why you would want to go to a bbq when you have a sore throat, bad cold and are feeling shit anyway. I'm sure everyone will be thrilled at you sneezing all over their sausages!

Well there is a cold doing the rounds, as lots of people having covid and cold symptoms coming back negative in PCR tests near us (SE England). So you probably don't have covid. But also some people are having the cold very badly - perhaps a year of no germs has lowered immune systems! So I wouldn't want to spread it.

Stay home, and book a PCR for peace of mind. But others are right - chances of 4 tests being wrong is very very unlikely.

At work, my colleagues all had negative lateral flows all week when they had awful 'colds' one went to get a pcr as they felt so ill by gross at and they all had covid. Bubble burst -all poorly!

Friday! Not gross at!!!

@Tippexy

A cold and a sore throat are not indicative of Covid. Do you usually have anxiety?

Wrong and rude

Just been to a walk thru for a PCR test.

I would get a PCR test ASAP, I know several people whose only symptom was a sore throat and they tested positive. If you can get one this morning, they will tell you results can take 48 hours but they seem to come back the next morning so you will know before BBQ. Although I don't think I would go if I had a cold and sore throat anyway.

@bellsoflemon

Just been to a walk thru for a PCR test.

Cross post, fingers crossed for you

Also how lovely are the people at the testing sites!
Made me feel so comfortable doing my test, they were super friendly and really caring!!

I had covid, probably the kent variant as it was over xmas and my symptoms were sore throat and feeling tired. Nothing else really, barely registered a temp for 5 minutes.

So could be covid, but also that describes my yearly hayfever symptoms and pollen is very high this week.

Lateral flows only pick up a very high viral load so there are a lot of false negatives.

I had a patient on the phone earlier this week who kept ringing with his headache and sore throat and we kept asking him to get a pcr test. He kept doing lateral flows instead and didn't isolate himself or his family. Eventually on the third time of being asked (6 days after symptoms began) he went and got his PCR which is positive. His whole family are positive including elderly parents who live with him and are double vaccinated. Two bubbles in a local school broken because he just wouldn't get tested properly. Merrily walking around spreading it for at least 6 days.

The most common symptoms of Delta variant are headache, sore throat and runny nose. Well done for getting tested.

I've just looked into this. According to the info I've seen, when done right the lateral flow tests are 57.5% likely to be correct.
That's 0.03% likely to give a false positive, so let's say around 40% will be false negatives.

So test 1: 40% false negatives
test 2: 40% false negatives
test 3: 40% false negatives
test 4: 40% false negatives

So the chance of getting 4 false negatives on paper is (0.4)^4=0.0256, so 2.56%
So it's a small risk, but not unknown-that works out to be about 25 people in every 1000 will have 4 false negatives.

But: It depends why they're false negatives. If it's just accuracy of test, that is one thing. But if it's operator error, or something to do with the way covid has reacted in your body (don't know if that's a thing) then it may be that if you have one false negative it's much more likely that you have more false negatives.

However I'd also twist it round. If false negatives from lateral flow are also due to not having enough virus at that point, then taking 4 over subsequent days, you're likely to catch the time when you have more virus and are likely to be shedding it, so I'd suspect that 4 false negatives over a few days would be much more accurate than the figures.

Good luck with the PCR test.

Apologies if I've missed it, but I don't think anyone has answered your likelihood question. There are some details in this bmj article www.bmj.com/content/bmj/369/bmj.m1808.full.pdf that suggest the false-negative rate might be as high as 29% (or as low as 2%) even taking the higher figure the probability of 4 independent tests all being false negatives would be 0.7%, given you don't have the classical symptoms it seems pretty unlikely you have Covid.

Having said all that in terms of the "should I go?" question if you are feeling awful would you ordinarily have gone? I probably wouldn't for all the reasons others have said.

@sussexman

Having said all that in terms of the "should I go?" question if you are feeling awful would you ordinarily have gone? I probably wouldn't for all the reasons others have said.

I wouldn’t say I feel awful, more that I have an awful cold - really blocked and runny nose, sneezing, sore throat, thick head kinda thing.

I’ve messaged my family to say I won’t go, but they’re all still insisting I go!!

@Tippexy

A cold and a sore throat are not indicative of Covid. Do you usually have anxiety?

Sadly according to the Zoe app, these are exactly the most common symptoms they are finding that young people who have caught the delta variant have. Most common are sore throat and runny nose with fever only the third most common and cough after that.

OP I wouldn't go, it's just not worth the risk

@yomommasmomma

Sadly according to the Zoe app, these are exactly the most common symptoms they are finding that young people who have caught the delta variant have

It was my understanding that the Delta variant was more severe so wouldn’t it present with more
severe symptoms? Ie high temp and bad cough.

Dd did daily lft as close contact all negative- test and trace suggested pcr, it was positive

[quote bellsoflemon]@yomommasmomma

Sadly according to the Zoe app, these are exactly the most common symptoms they are finding that young people who have caught the delta variant have

It was my understanding that the Delta variant was more severe so wouldn’t it present with more
severe symptoms? Ie high temp and bad cough.[/quote]
After a few days it may get more serious. Chest and cough symptoms come later.
From a virus point of view surely it’s more successful if it’s mild for a few days to be spread around before the patient gets so ill so can’t move around. That’s how viruses succeed, they evolve to make themselves more spreadable.

You can't go now you've done a PCR test, you need to isolate until you get the result. It probably will be negative, but if it's positive you'll have to explain to the track and trace people why you went to a family party.

I wouldn't be impressed at you rocking up full of a cold either. Just because it's not covid doesn't mean everyone should be exposed to it!!

I’ve been in a similar position. I came down with cold symptoms this week. (sinuses headache, sore throat, generally feeling blah) I’ve fully vaccinated and post 3 weeks for the 2nd vaccine. I didn’t have any of the 3 symptoms that would indicate I needed to PCR test. So I’ve just done a LFT everyday, all negative. I figured as I was symptomatic my viral load would be big enough for at least one of them to show as positive if it was Covid. So given all the negative tests, the fact I’m fully vaccinated and that I had none of the warning symptoms that was enough for me to assume I was negative.

@MargaretThursday

I've just looked into this. According to the info I've seen, when done right the lateral flow tests are 57.5% likely to be correct. That's 0.03% likely to give a false positive, so let's say around 40% will be false negatives.

So test 1: 40% false negatives
test 2: 40% false negatives
test 3: 40% false negatives
test 4: 40% false negatives

So the chance of getting 4 false negatives on paper is (0.4)^4=0.0256, so 2.56%
So it's a small risk, but not unknown-that works out to be about 25 people in every 1000 will have 4 false negatives.

But: It depends why they're false negatives. If it's just accuracy of test, that is one thing. But if it's operator error, or something to do with the way covid has reacted in your body (don't know if that's a thing) then it may be that if you have one false negative it's much more likely that you have more false negatives.

However I'd also twist it round. If false negatives from lateral flow are also due to not having enough virus at that point, then taking 4 over subsequent days, you're likely to catch the time when you have more virus and are likely to be shedding it, so I'd suspect that 4 false negatives over a few days would be much more accurate than the figures.

Good luck with the PCR test.

This is garbage - please DO NOT post about things you have no understanding about!

You're treating them like tossing a fucking coin.
If one test doesn't register a +ve, the next test will give exactly the same result, unless the first test failed due to user error.

[quote bellsoflemon]@yomommasmomma

Sadly according to the Zoe app, these are exactly the most common symptoms they are finding that young people who have caught the delta variant have

It was my understanding that the Delta variant was more severe so wouldn’t it present with more
severe symptoms? Ie high temp and bad cough.[/quote]
No, it's not more severe. It's more transmissible. Spreading like wildfire in some areas, particularly in schools.