Why do you think people get a positive lateral flow and then a negative PCR?

[MilkBread]

Has the reasoning ever been explained? Especially after the lab debacle?

It just seems to be happening so much. I would believe they were just false positives if there was no close contact, but most of the cases I’ve heard about on here and in real life were after close contact.

I know. They've gone very quiet on the matter.

I know someone the other way around. Negative lateral flow and then positive PCR

What I have read was that lft is actually good at detecting presence of the virus.

So, if you had virus present on the site you swabbed, like virus was stuck inside your nose because of the close contact, you may get positive lft, because the test detect the virus.
But if you can fend off the virus before it infect you, then by the time you take pcr, you would be negative, because you are not infected.

I'm not an expert, and I don't know if this is true or not, but it was explained on other site, and it makes sense to me.

I had 14 positive lfts and 4 neg pcrs last month. Had symptoms of a cold, bit of a cough, headache and weirdly lightheaded for a few days. I definitely had something but will never know if it was covid for certain.

From what I read the lfts miss alot of cases but when they are positive, its really unlikely to be wrong. I think it's 0.4% chance of a false positive so mathematically it should be almost certainly covid.

I wondered if there is an unidentified variant that has enough mutations not to picked up on pcrs but the body produces antigens that are still recognised by the lfts. Or there's a normal cold virus that produces similar antigens and the lfts are picking that up instead. Who knows!

Possibly they have eaten something or drank something that reacted with the test no-one can say for sure

There’s no test that doesn’t fail sometimes and thousands are being taken.

We have had several of these at my school recently. In the majority of cases people took a second PCR which was positive. Maybe the new LFTs are very sensitive?

Thanks for your thoughts. My main reason for asking is that a friend is coming to stay tomorrow. She and her family had positive lateral flows last week. But she’s just phoned to say thank goodness her PCR was negative so it isn’t Covid and she can still come.

I’m aware of the issue through mumsnet but no one else seems to be

False positives are more unusual than false negatives.

It's more likely that the PCR was wrong they are not 100% accurate.

So most likely your friend did/does have COVID

^^ especially when her WHOLE FAMILY got positive LFTs. Are all their PCRs negative too?

Yes all PCRs negative! Just so odd - she can’t understand why I’m wary!

If her entire family have had positive LFTs then no way would I be having them to stay.

Did they have symptoms to test?

I think there's under reporting of this though. I had a positive LFT and negative PCR (no symptoms). I never registered it or reported the positive LFT so who would know - I imagine a lot of people have done the same.

Oh crikey, don't let them in! The immensa thing proved that negative PCR after a positive lateral flow was almost always an incorrect pcr result.

I got a positive LFT this morning. Had my booster yesterday and it seems that while PCRs definitely can't be affected by a recent vaccination a LFT possibly can be. Nobody seems to know for sure though.

To make me look bad at work, that's why!
(negative PCR came back. Why do I feel so lousy?)

I've commented on similar threads but we had a positive household case confirmed with a PCR. My DC then had two faint positive LTFs followed by two negative PCRs. I think that my DC did have it because of the very low rate of false positive LTFs along with the fact that we had a case already in the house. None of the tests were done straight after eating or drinking.

I read that if you have a positive LTF and circumstances that suggest Covid too, it makes sense to isolate and go by that regardless of the PCR result. E.g. circumstances like ours with a household case or actual symptoms.