Positive lateral flow test negative pcr test

[potterface29]

I'm so confused! Took my first ever lateral flow on Saturday, as my daughter who's at nursery, came back positive. Im 32 weeks pregnant so this terrified me, took another that also came back positive! Booked a PCR test for the whole family, which took until Sunday evening to come back, negative for me and my husband and daughter. However can still get a positive result on a lateral flow. Called nhs 119 and they just advised me not to take the rapid test anymore! But couldn't tell me why I was getting positive results on rapid test?

Mostly worried about the baby and pre term labour , but also don't want to spread the virus unknowingly. I'm very careful being pregnant and don't really go anywhere other than supermarket at the dead of night.

Anyone else in a similar boat? Anyone had Covid late in pregnancy like third trimester?

Thank you
Many thanks

The PCR test is considered the gold standard and is highly sensitive, so if that came back negative I think you're okay.

The PCR is the one to follow.

Talk to your midwife. Although the PCR is the best we've got, it can give 30% false negatives. I'd be tempted to book another one in your position.

Even if you have got Covid, the chances are you and baby will be fine 💐

I thought that you only had a pcr test if you had symptoms and lft if asymptomatic as they test for different proteins. That's my understanding. Also false positives on LFTs are very very low. So if you are asymptomatic and are testing positive on LFT I would have thought you certainly have Covid, especially if you are positive on repeat tests

I think you probably had a false negative on the PCR

If your daughter was positive you have to isolate anyway. I'm guessing she had a pcr? Whole household needs to isolate for 10days

Apologies I just realised I missed a comma haha you were positive and not your daughter

@XiCi that's not correct. The lateral flow test can pick up asymptomatic AND symptomatic cases, but is only recommended as a screening test rather than diagnostic test, because it's far less accurate than the PCR.

Positive LFTs done at home should be confirmed/negated by a PCR test, as the PCR test is gold standard.

However, it does sound a bit weird that you've had so many positives on the LFT, OP - the false positive rate is supposed to be about 0.3%. I think you've either had a false negative PCR, which isn't unheard of, or you've maybe got a weird batch of LFTs. If I were you I'd err on the side of caution and either go for another PCR test or just self isolate.

By the way, you shouldn't take the whole family to get PCR testing if it's just you who's had the LFT - should be just you following it up.

Given that the false positive rate on the LFTs is so low its seems much more likely that you have a false negative on the PCR so would get another one. Try not to worry. I know its easier said than done, I tested positive on Wednesday and for me the anxiety caused by the media reporting was far far worse than the covid symptoms

I’d try in a couple of days. I had a positive LFT then a negative PCR. I then felt really poorly and did another PCR which was positive.

I would repeat your PCR in 2 days, isolate until then, the LFD is telling you you’re infectious, possibly very early stages and not picked up on the PCR yet

The school kids were asked if they’d had COVID in the last 90 days as it will give a positive LFT maybe you’ve had it and not known in the last 90 days. Although I’d have thought that would also show up on PCR...

The school kids were asked if they’d had COVID in the last 90 days as it will give a positive LFT

LOL - no it won't!

@mightyducks

I would repeat your PCR in 2 days, isolate until then, the LFD is telling you you’re infectious, possibly very early stages and not picked up on the PCR yet

Total nonsense

However, it does sound a bit weird that you've had so many positives on the LFT, OP - the false positive rate is supposed to be about 0.3%.

But false negative is not a random event, taking the test again only changes the odds of changing the result for random things. Not (if the tests are all from the same batch/storage) from test problems, or from another coronavirus, or from something in the mouthwash you use, or …

If the LFT was just randomly false positive then simply doing two tests would be useful, but it's not, so it's pointless.

The PCR test is the one to follow - it is FAR more sensitive to the virus that the LF so if you were infected, then the PCR would certainly show it.

Why you are getting so many +ve LF's is another question - contaminated tests??

The LTF can produce a positive result up to 90 days from infection- could your daughter have had the virus and been asymptotic?

Just realised in my first post, it sounded like my daughter came back positive. So to clarify, my daughter had a slight stuffy nose, which we assume is a cold, but being covid world, you can't be too careful, so i took a lateral flow test just because we are meant to do it as a household to catch asymptomatic transmission. Both lateral flows I took that morning came back positive, which we followed up with PCR on same day which came back negative for all of us.

@vodkaredbullgirl @MissConductUS Thats what I was told by 119, told me to not isolate and not take another lateral flow for 90 days

@XiCi @BabycakesMatlala Ive never heard about lateral flows testing for protein, just wish they gave you more information about the tests and explained what to do in this situation.

@notrub My husband took one of the LFT the same day and his came out negative. The only difference is I am pregnant and he is not.

I have booked myself in for another PCR test tomorrow just in case I am too early on in infection. Thank you for all the comments.

@potterface29

Just realised in my first post, it sounded like my daughter came back positive. So to clarify, my daughter had a slight stuffy nose, which we assume is a cold, but being covid world, you can't be too careful, so i took a lateral flow test just because we are meant to do it as a household to catch asymptomatic transmission. Both lateral flows I took that morning came back positive, which we followed up with PCR on same day which came back negative for all of us.

@vodkaredbullgirl @MissConductUS Thats what I was told by 119, told me to not isolate and not take another lateral flow for 90 days

@XiCi @BabycakesMatlala Ive never heard about lateral flows testing for protein, just wish they gave you more information about the tests and explained what to do in this situation.

@notrub My husband took one of the LFT the same day and his came out negative. The only difference is I am pregnant and he is not.

I have booked myself in for another PCR test tomorrow just in case I am too early on in infection. Thank you for all the comments.

My husband took one of the LFT the same day and his came out negative. The only difference is I am pregnant and he is not.

So that rules out a bad batch of testing - so there are ONLY three explanations left.

1. The PCR was a false -ve.

2. Your pregnancy makes the LF's give false +ve's and your daughter by chance got a false LF +ve - presumably she only took ONE LF test?

3. Both you and your daughter have something that isn't covid, that makes you test +ve.

The results of the second PCR will be interesting.

A friend (healthcare worker) always returns positive lateral flows with negative PCR's. It's unusual but 'normal' for her and there are reports across the country of this. She had an explanation from a medic with expertise in microbiology as to why it was happening which completely put her mind at rest but she wasn't able to explain it to me. So it does happen and if the PCR is negative, it's highly unlikely you have Covid.

So I had another pcr test done on Thursday, results came back this morning as negative! Just wanted to post in case anyone is in a similar situation and as confused as I am! So two negative pcrs, guessing the chance of those being both wrong are quite slim!

I'd assume you'd had COVID asymptotically and haven't got it any more. You can test positive on the LFT up to 90 days after a COVID infection, but you'd test negative on the PCR

@hedgehogger1

I'd assume you'd had COVID asymptotically and haven't got it any more. You can test positive on the LFT up to 90 days after a COVID infection, but you'd test negative on the PCR

I'd assume you'd had COVID asymptotically and haven't got it any more. You can test positive on the LFT up to 90 days after a COVID infection, but you'd test negative on the PCR

People keep repeating this for some reason, but it's complete nonsense!

The LF is FAR less sensitive than a PCR test. There is no chance it will ever pick up a +ve case that a PCR would miss.

@potterface29

So I had another pcr test done on Thursday, results came back this morning as negative! Just wanted to post in case anyone is in a similar situation and as confused as I am! So two negative pcrs, guessing the chance of those being both wrong are quite slim!

Reading around and it seems some people do give +ve LF results without having covid - so probably not much point in you taking them again! You'll have to rely on the LF results of people around you or your own symptoms and go straight to PCR in future.

At least you got the all clear though, which must feel good!

Apparently the LFTs are very sensitive and can pick up on other things and give a false positive. NHS advice here -
If your Lateral Flow test result is positive this will need to be confirmed with a PCR swab test. This is as the Lateral Flow test device is very sensitive and therefore may report positive results when COVID-19 is not present. The PCR test is better at picking up the COVID-19 test specifically and therefore this is used to confirm a positive result

Its so strange that you kept getting positive results, it must be picking up on something else specific to you. Must have been really stressful not knowing!