Positive Lateral Flow…then two negatives , not sure what to think!

[Keepgoing88]

Ok so I’ve posted a lot today but I’ve got myself in a bit of a twist. I got what I thought was a faint positive (def a line within 30 mins just quite faint) . Given that everyone I live with bar 1 have confirmed Covid I assumed it must be right so booked and went to PCR. I’ve not been feeling great had headache but that’s it really. Anyway… as the lateral flow was faint I thought oh I’ll just do another one whilst I wait for the PCR result. Anyway this one was clearly negative , like no trace of a line. DH said it must be a duff one so do another , I did and that is also negative! Could it be a false positive the first time? I feel silly now rushing out and getting a PCR but I am living with Covid positive kids and husband so I assumed that I just had it!

You did the right thing, lft tests are just not accurate enough - they are only designed to pick up asymptomatic cases that would otherwise go undetected, and to try and halt some asymptomatic cases that are unwittingly spreading COVID in the community.

You’ve had 1 positive lft, you have positive cases in the house - a pcr test is what is needed.

The lateral flow tests are very insensitive. And it comes down to luck sometimes with swabbing technique/virus presence. You’ve done the right thing getting a pcr.

Place marking. I’m curious about your PCR. Hope you come back to tell us OP.

@everythingthelighttouches I will update the thread.

The lateral flow tests are rubbish and have a high chance of giving you a false negative. So what you describe sounds plausible - that you may have covid and one 1 out of the 3 tests show that.

The tests are basically junk.

Another faint positive on lateral flow (I’ve been asked to take part in a study by the test centre). Given the situation with most family members positive I will probably get a PCR again in a few days if this one negative. I haven’t coughed a lot but still feel rough and woke in the night to cough a little

I dont understand. Why aren't you arranging a PCR test today? (Or yesterday?)

What we call your “pre-test probability” is high. This means that you aren’t taking a test just as routine but there’s extra information which means you are more likely than the general population to have COVID.

It’s for this reason that they don’t recommend LF tests in symptomatic people - they actually work better in people with symptoms - but are still highly unreliable and they don’t want people with a high pre-test probability to give themselves the “all-clear” because that would increase the number of people circulating with COVID-19.

Add to that the inconsistency of self-swabbing and it’s no surprise that you have inconsistent LF results - even with professionally taken samples I see cases of multiple negative tests in hospitalised patients who later go on to have COVID confirmed through imaging.

I think the PCR will come back positive. If it doesn’t I would retest.

@Ginmakesitallok

I dont understand. Why aren't you arranging a PCR test today? (Or yesterday?)

OP is waiting for the result of a PCR

@Ginmakesitallok just look at my original post

I know someone who had the classic symptoms, double vaccinated, took a LFT and was negative, kept feeling worse so took a PCR and it was positive.

In a nutshell they aren't that accurate!

@Gunpowder thanks. That’s what I intend to do :)

@Ginmakesitallok

I dont understand. Why aren't you arranging a PCR test today? (Or yesterday?)

Did you read the OP?

I keep hearing about LFTs giving false negatives! Makes me feel a bit iffy about relying on them.

I had 5 negative laterals. My PCR was positive. I was poorly with flu like symptoms. Definitely get a PCR if ANY symptoms, no matter how mild

Thanks @Shelby10 I have had one, awaiting results. I used to do regular LFTS for work but I would have probably gone to work with my squinter of a line this morning as you can hardly see it I doubt I would have noticed had I not stood in a place with really good light!

@Firstbornunicorn the lateral flows aren’t supposed to be relied upon - their only purpose really is to catch asymptomatic or presymptomatic cases to avoid those people walking around contagious in the period before they get symptoms (and some never do).

Using any of these tests to check you are safe isn’t really appropriate. None of the tests can pick up Covid-19 where none is on the swab and there are lots it reasons why a COVID + person may test negative (poor swabbing technique, recent eating/ drinking, low viral load, too early amongst others)

@MaximumVolume I understand that, but it’s undeniable that they ARE being relied upon. A friend of mine was told by the school that her symptomatic daughter could attend after a negative LFT. I know that’s not right, but it does show that people have more faith in them than perhaps they should.

Lateral flows are quite effective at picking up people who are infectious, ie those who have a high viral load and are in the first week of infection Peto et al / UK Lateral flow oversight team 2021
The problem with PCRs is that they detect viral RNA particles being cleared out by your body when you are no longer infectious. Reviews have found that most people are infectious (ie shedding viable virus that can be cultivated in a lab) for under a week from first symptom onset; this text review of infection dynamics by Cevik et al found that the average patient tested positive on PCR for 17 days (some for up to 83 days!), but that infectious virus could only be cultivated in the first week of symptoms generally, with the outside case being 9 days. I've since seen research suggesting that people who are severely immunocompromised can shed live virus for longer. So the fact that LFDs don't pick up all the cases that PCRs will detect doesn't necessarily mean they're "not as good" ; it depends which cases you're most keen to detect.

When you test and get a faint positive, it could be because you're at the start of the infection and more antigen will be detectable later on, or because you're on the downward slope and getting over it, in which case you probably would have got a stronger positive the day before. I've observed someone getting a good progression of daily LFD results, from clear, rapid positives tailing off through faint positives that took time to develop, then negative.

I've got a similarish dilemma OP. Got a positive LFT yesterday, panicked and took another, it was positive too. Booked a PCR and got tested a couple of hours later. Result came in this morning - negative. Out of curiosity tried another LFT and got another faint positive. I don't feel particularly ill but like a mild cold is brewing sort of feeling since last night. I can't figure out if I'm supposed to be worried or not

@BastardMonkfish omg I feel like that too. How weird is that I wouldn’t have thought 3 LFT would be wrong. If I was you I would do another in a couple of days … that’s what I intend to do as I’m sure I’ve got it. 3/5 have recently confirmed positives now in my house x

@BastardMonkfish

I've got a similarish dilemma OP. Got a positive LFT yesterday, panicked and took another, it was positive too. Booked a PCR and got tested a couple of hours later. Result came in this morning - negative. Out of curiosity tried another LFT and got another faint positive. I don't feel particularly ill but like a mild cold is brewing sort of feeling since last night. I can't figure out if I'm supposed to be worried or not

PCR sensitivity is about 95% currently and LFD around 75%, so I'd assume you're the 1 in 20 where PCR did not pick up an active infection. You won't have got false positives from 3 LFDs; the chances of that are vanishingly rare. In your shoes I'd act as if I was infectious and self-isolate, and allow a margin of a couple of days after the LFD turns negative.

Nb I'm a health researcher & have been working on Covid projects. If I got 2 positive LFDs I'd definitely treat myself as positive regardless of what the PCR result was. You could request a second PCR but personally I would just consider myself positive.

The UK Lateral Flow Oversight team found LFDs were actually very sensitive at picking up cases with high viral loads who got a strong positive (low Ct value):
"There was a strong association between viral load detection (RNA copies/mL) determined through RT-PCR and viral antigen detection by LFD (Fig. 1). Confirming earlier analyses, sensitivity of LFDs is highest in samples with higher viral loads [19."

They also note :

there is an expanding body of evidence that suggests viral load/antigen is important as individuals with the highest viral loads are the most infectious, 20 and the presence/absence of viral antigens determined by LFDs is more strongly associated with a viral culture than RT-PCR positivity 21.

In other words, LFDs may possibly be better at picking up infectious cases than PCR, although more research is needed to explore this.

When you hear about LFD "kit failure", that's usually where not enough fluid is transferred to the LFD test strip for it to function. High failure rates don't mean that other results aren't valid, just that you can get a lot of wastage.

Update - I got my Covid result back from the PCR it’s positive.