Positive LFTs but negative PCR twice

(130 Posts)
DaxtheDestroyer Thu 23-Sep-21 06:57:18

So confused! My DC tested positive on an LFT, we booked a PCR which was negative. When we got the result we checked with another LFT (completely different batch) which was even more strongly positive. Repeated PCR - negative again.
So what's going on? There must be something causing the positive LFTs, there are loads of cases at school at the moment. Anyone had this happen? Just so confused as to what's the right thing to do

OP’s posts: |
Whinge Thu 23-Sep-21 07:01:05

2 positive LFT and the result being stronger the second time would suggest it's very likely she has Covid. What's the timeframe for testing? As you may have tested too early for a PCR to show a positive result.

Okwotnext Thu 23-Sep-21 07:07:36

Same problem for me. My son confirmed covid case last week on lft and pcr. He had it. He was clearly unwell. I lost my sense of taste on Monday. I did a lat flow. I show strong positive on lat flow since Monday and each day since. I have received a second negative pcr today. This is happening lots in our area the south west. It is nuts. I am convinced I have it due to the fact I have a main symptom, have positive lateral flows and also my son was a confirmed case. The exact same happened to my daughter tail end of last week.

JasonMomoasgirlfriend Thu 23-Sep-21 07:09:23

Are you waiting 30+ minutes after food and drink before testing?

JasonMomoasgirlfriend Thu 23-Sep-21 07:09:42

For doing the LFTs I mean.

Okwotnext Thu 23-Sep-21 07:11:14

As to what to do ….with my daughter I kept her off school a week so she isolated 7 days. Then school said for her to go back as pcr negative. My work will also expect me in but I plan to argue it. I feel fine but it’s not right to go in with a symptom and positive lat flow in my opinion.

Okwotnext Thu 23-Sep-21 07:11:41

Yes done first thing on waking.


Miserablewithweight Thu 23-Sep-21 07:12:51

This is happening to us too! Also south west @Okwotnext!

Son has had two very strong positive LFT but PCR came back negative. Took him for a re test yesterday so waiting for that result … he’s clearly unwell with all ten classic symptoms. His class and school has so many cases and his step sibling also tested positive on Monday!

When we did another pcr yesterday they had us chat to test centre manager as they recognised we’d been in recently. She said
They’ve had loss of people with positive LFT and symptoms testing negative or inconclusive so they’re investigating that.

I’m not sure what’s going on?! If it’s something new or if the pcr tests are somehow wrong?!

DaxtheDestroyer Thu 23-Sep-21 07:19:19

Hmm we are also south west!
She doesn't have any symptoms at all but there are quite a number of confirmed cases of close friends at school. Yes the LFTs are more than 30 mins after food and drink. I've emailed the school for their advice 🤷🏻‍♀️ I suppose I keep her at home until I hear from them at least

OP’s posts: |
CiderWithLizzie Thu 23-Sep-21 07:21:43

That has happened to my colleague too. Both children positive on LFD and PCR but he was only positive on LFD. Two PCRs negative in spite of covid symptoms. Luckily our boss allowed him to isolate. Also south west confused

JasonMomoasgirlfriend Thu 23-Sep-21 07:22:16

But are you 100% sure no juice etc being drunk on the sky?
Cause on tiktok it's well known for kids to falsify the tests to get time off school!

Yellow85 Thu 23-Sep-21 07:22:37

Lateral flows test for your bodies immune response to covid, whereas PCR test for the active virus. Highly likely your sons had it asymptomatically and his immune system is still hosting the antibody proteins even though he no longer has the active virus.

Okwotnext Thu 23-Sep-21 07:24:57

Sorry to hijack thread but this was on school WhatsApp “ What did school say. So many cases like this now. Another one on y9:

"Initially had cough and headache. Then next main symptom (along with the cough) was really sore eyes when he moved them. He has tested positive 6 times on lateral flows since Sat but 4 PCRs all negative! But as he has covid symptoms we are keeping him off this week to be safe". This is common example. I’m told false positives on lat flow are unlikely suggesting pcr not detecting something.

Okwotnext Thu 23-Sep-21 07:29:07

But I’m a teacher. I test all the time. I don’t want to isolate. It’s a pain. I’ve gone from negative consistently to positive consistently with a confirmed case in house and a known unusual symptom. Pcrs then negative. I think pcr is wrong and honestly starting to wonder if there’s some mutation pcr is not detecting.

LegoClone Thu 23-Sep-21 07:31:27

I've experienced a similar situation although did eventually get a positive PCR result.

DC had a positive LTF followed by a negative PCR. Although DC had very mild symptoms (not the main covid symptoms) we assumed it must have been a false positive on the LTF and would have sent DC into school had it not been a Saturday.

DC did another LTF which was negative, followed by a positive LTF on the Sunday. Back for another PCR which returned a positive result Monday morning.

Talking to others i have heard a few recent cases of positive LTFs being followed by negative PCR results (in one case several times), both in people with and without symptoms.

Reading the available research suggests that false positive results on LTFs are really rare, unlike false negative results which are very common. This does make me wonder if something is going wrong with the PCR testing. I'm also in the south west.

DaxtheDestroyer Thu 23-Sep-21 07:35:03

Definitely no juice being drunk on the sly. First test was immediately after getting home from school (testing as there was an outbreak in the year group). Second test was while she was isolating in her room so all drinks being provided by us. Just done a third, will see what that says.

OP’s posts: |
Whinge Thu 23-Sep-21 07:36:14

Just done a third, will see what that says.

I'm not a gambling person, but i'd bet on it being positive.

Wagedogsbody Thu 23-Sep-21 07:52:08

This happened to me too I did a LF - positive was in shock so did another 3, all positive PCR - Negative I called NHS they said go off PCR. The next week i went back to twice weekly testing - positive again - off for PCR Negative. This has happened to two other families in my village. The only difference is that it was once i started using the newer LF thats just go up your nose (flexflo or something like that) I got a pack of the old style (nose and throat) from my pharmacy and bang.....back to very clear negative results. I dont trust the LFs as far as i would chuck them...but im still doing them.
My son tested positive last week (PCR - he is 8) and to show my younger son it's not so bad he did a LF infront of him (the newer style) guess what? It was negative. He clearly has it as he has a pos PCR, headaches, sore throat. Its really very confusing! NHS said go with PCR every time.

Miserablewithweight Thu 23-Sep-21 09:19:54

Our 2nd test just came back negative called the school (which has a massive outbreak) that they've been advised by our testing centre they think they have a dodgy batch if PCR testing kits as they've had so many people with positive LFT and all the classic symptoms come back negative

YourKidsIf Thu 23-Sep-21 09:26:29

Imagine if that’s true about the dodgy batch! Makes complete sense but all those people mingling who are positive but have had a negative result

noideawhat Thu 23-Sep-21 09:28:11

We're also in the South West & having similar issues. School advised us this morning to get re-tested with another PCR as they're hearing of lots of issues locally.

DaxtheDestroyer Thu 23-Sep-21 09:33:57


*Just done a third, will see what that says.*

I'm not a gambling person, but i'd bet on it being positive.

Well done Whinge, you win! Positive again, albeit much fainter than yesterday.

We've heard rumours about faulty batches (of LFT rather than PCR) so have used different sets of LFT each time.
School have advised keep them off for now. There's clearly something causing the positive LFTs given the rest of the family are also LFTing daily and we've all had negatives each time.

OP’s posts: |
zebra80 Thu 23-Sep-21 09:34:32


Lateral flows test for your bodies immune response to covid, whereas PCR test for the active virus. Highly likely your sons had it asymptomatically and his immune system is still hosting the antibody proteins even though he no longer has the active virus.

@Yellow85 That's not the case - both LFTs and PCRs test for the antigen (the virus) not the antibody, it's just that lateral flows are less sensitive - so very weird that people are having repeat positive LFTs with negative PCRs and symptoms.

Antibody tests are bloods that have to be sent off and processed in a lab.

DaxtheDestroyer Thu 23-Sep-21 09:36:48


Imagine if that’s true about the dodgy batch! Makes complete sense but all those people mingling who are positive but have had a negative result

I know of at least 5 people personally at school who've had this happen. Some with clear symptoms, some with no symptoms. Some have stayed off anyway others have done as guidelines instruct and carried on.

OP’s posts: |
Yellow85 Thu 23-Sep-21 10:00:33

That’s not correct @zebra80 a LFD detects a COVID-19 antigen, that is produced when a person is infected with COVID-19 it doesn’t test for the covid virus itself. The antibody test is completely different.

I probably used the wrong word (antibody), but effectively the LFD looks for pathogens/bio products produced when someone is infected with covid.

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