Multiple positive LFTs, negative PCR

[FromTheAshes]

As the title says, really. Had anyone had this before? I have another PCR test booked for this morning after getting yet another positive LFT this morning.

Sounds like you probably had a false negative PCR. It's possible if the sample is a bit rubbish. Make sure you don't eat or drink anything before the test (think they recommend half an hour, but longer if poss) as contamination could easily damage the sample.

@PlantDoctor quite possibly. The swab for the pcr is huge compared to the LFT swab, I couldn't do anywhere near as thorough a job as I do with the LFTs. Will see how this morning's PCR goes, hopefully the results will come back quicker than my last test (3.5 days)!

Hope it comes back quickly for you!

I would ignore the negative PCR and treat as positive. There are plenty of ways the PCR could have been a false negative - poor swabbing is one, presence of PCR inhibitors in the sample e.g. in blood, RNAses in the sample from snot. The control for the PCR test is a highly expressed human gene (i.e. You expect there to be many copies in the sample), if you've got partial inhibition of the PCR reaction or partial degradation of the sample by RNAses then you can get enough amplification of the control but not enough amplification of the viral RNA. The false negative rate of LFTs is actually tiny so I've no idea why we're letting people carry on as normal with a subsequent negative PCR.

PCR done, I was ahem extremely thorough 🤣 just a waiting game now.

Thanks for that extra info @QueenStromba, that's really interesting to know. I love the science behind these things! Hopefully today's test is more accurate, don't want work losing patience with me so soon after the directive to return to the office.

I have heard of the opposite several times (more then one negative LFT alongside a positive PCR) but not this scenario.
Must be a mis-test, surely.

Negative! PCR results came through at 4am. It was as thorough as a test could possibly be. I really don't understand. I know what a negative LFT looks like, I do them daily. The only positives I've ever had have been from Monday this week. Not the strongest, granted, but if the same line had come up on a pregnancy stick I'd have been celebrating.

They don't photograph too well, but the attached is (top to bottom) Monday, Tuesday, Wednesday, Friday. I used different batches, so it can't just be a dodgy box. All tests taken on waking, so no eating, drinking, toothbrushing beforehand etc.

I think the LFT are negative - I think you need two lines for a positive.

The first line (C) is the control and the second (T) is the result

www.gov.uk/guidance/understanding-lateral-flow-antigen-testing-for-people-without-symptoms

Those LFT are all negative. You only have a control line. You would have two lines for a positive test, like a pregnancy test.

I can’t see any lines?
This is the positive lateral flow we got yesterday (in between 2 negatives). Waiting on PCR results now

Are you using the same bottle of fluid?

There are definitely lines there, as I say they don't photograph too well, perhaps try adjusting your brightness. Tuesdays and Wednesdays are the easiest to see in my picture. If they'd been pregnancy tests I would definitely have been celebrating. All came up within the 30 minute mark, the photos are at exactly 30 minutes. As it says in the instructions, even a faint line at the 30 minute mark is a positive. My dad's care home wouldn't have let me in with those results.

For the record, this morning's LFT was negative, as was every single test I took in the months before.

@Angrymum22 no, as I mentioned, I've used different batches across the week. It's a fresh test each time.

I can see very feint lines second lines in a couple of those tests. I would say the lateral flows are positive.

How strange your PCRs are coming back negative.

I understand false positives are very rare. It's false negatives that are the issue.

I think I'd phone 119 or my GP for advice.

How do you feel OP? Do you have any symptoms?

Very odd. I can see the second lines too (just). My friend got a positive pcr after a similar looking lateral flow test.

@Lindy2 thank you, glad someone else can see them, I know a lot of people are expecting to see a line as strong as the control but that's often not the case. I'm double vaxxed and have had a mild head cold all week with a lot of the symptoms that the Zoe app lists as the main symptoms for double vaxxed people. Work are going to want me to act on the negative pcr, so daughter back to childcare, me back to the office.

Is it possible you have another mild virus that isn’t covid that the LFT test is detecting but the PCR being more accurate is discounting?

I tried tweaking the contrast on your image and I can definitely see a second line on all 4 tests.

Maybe it’s out of the 4-5 day window for the pcr test to pick it up?

I thought the test had to be done within a certain time scale

Are they all from the same pack of LFTs? Maybe a dodgy batch

will you keep your distance if you need to return to work op?

I would probably behave as though the PCR was positive and isolate for 10 days. I know they say line is a line but I'm struggling to see them on screen. The negative ones never have a hint of a second line though so trust your gut if you can see it. My DCs positive lateral flow was very obvious by comparison.

I did wonder that @Santastealer, but can't find anything in Google to back that up. Great picture tweaking by the way, thank you very much!

@User5827372728 I did my first pcr on Monday when I got my first positive LFT and started with my head cold. It took till the small hours of Friday morning for that result to come through, that's why I hadn't booked another until yesterday. I figured I'd I was still getting positives on LFTs it was strong enough for a PCR, plus they're saying you can get a positive pcr for 90 days after infection so I'm not so worried about timescales.

Not as much as I'd like @AbsolutelyPatsy.

I'd like to think my line faintness is due to being vaxxed but I think these things are just so variable you never can tell.

@CeeceeBloomingdale

I would probably behave as though the PCR was positive and isolate for 10 days. I know they say line is a line but I'm struggling to see them on screen. The negative ones never have a hint of a second line though so trust your gut if you can see it. My DCs positive lateral flow was very obvious by comparison.

That's a very strong positive! Do you know if they passed it on to anyone?

I've had the same OP, 2 positive LFTs (12 hours apart, second stronger and both stronger than in your pics), went for PCR

test same day (in a very hot car/carpark I might add) which came back negative. Now 4 days after the first LFT I'm getting runny nose, sneezing, diarrhoea so have ordered another PCR through the post to double check. Either way am isolating for 10 days from first LFT, but want to confirm for work.