Interesting LFT result

[StrongLegs]

Hi,

I wondered if I could ask for others' thoughts on some interesting LFT results?

I was a biomedical research scientist for nearly 20 years before I was a Mum and I think I understand how LFT works, but I could be wrong.

Our whole family have covid at the moment. We also all had it last March (2020).

Here we are in detail:

DS 11
March 2020 covid entirely resolved
Unvaccinated
cough and fever since Saturday this week
strong +ve LFT with result showing in under 2 minutes
+PCR test

DH
March 2020 covid symptoms entirely resolved
double vaccinated
very bad cold symptoms since Tuesday
-ve LFT
awaiting PCR test

myself:
Ongoing long covid since March 2020
single vaccinated
new flu-type symptoms since Tuesday
-ve LFT
awaiting PCR test.

I'm just puzzled about why DS's lateral flow test lit up like a firework, while both of ours are showing a definite negative result.

Do you think that means that our vaccinations are causing us to shed fewer virus particles? I would be really glad to hear what others think.

DH and I are both confused about why LFT picks up asymptomatic infections but not symptomatic ones. Bearing in mind that they picked up DS's symptomatic infection, but not ours.

Thanks!

Surely there’s no guarantee you and DH have it?

How do you know your whole family has covid if only your son has tested positive?

You could both not have covid?! Or not have covid yet?

Were you all tested last March? I didn’t think they were widely testing then

You don’t know you’ve got it. I’d wait for the pcr test before leaping to any conclusions. Lots of other respiratory bugs about at the moment.

DH and I are both confused about why LFT picks up asymptomatic infections but not symptomatic ones

You can’t say this. LFTs can pick up symptomatic infection. They can also miss it, the same as with asymptomatic infection.

DH and I are both confused about why LFT picks up asymptomatic infections but not symptomatic ones

Just though-have you totally misunderstood the reasons for the government telling people not to use LFTs for covid symptoms?

Ignoring the tests -- you all clearly feel a bit shit, so I hope you feel better soon.

LFTs are hit and miss, I've had 7 positives, some strong and some faint. All negative PCRs.

I now likely have covid (DM tested positive and we were exposed and now I have many symptoms) still get negative LFT.

DM is positive PCR and has had a mix of negative and positive LFT

I just think once symptoms hit, trust the PCR

There was a report recently saying LFT’s are nearly 95% effective for symptomatic cases. However this is relatively new research. LFT’s are around 48% sensitive to asymptomatic cases. Prior to this research coming out, it was thought that PCR’s are far more reliable and can also detect lower vital loads than LFT’s.

www.qmul.ac.uk/media/news/2021/smd/lateral-flow-tests-are-95-effective-at-detecting-covid-19-when-used-at-the-onset-of-symptoms.html

DD and her partner tested daily when they had 'hay fever' ( we'd bought some private tests at Xmas, so they used those). They tested strongly positive as soon as their symptoms got stronger ( still none of the big 3) and PCR was positive too. They were positive for four-five days during which time they both got better and then became negative. In their case it seems like it can pick up higher viral loads ( and therefore more infectious people). This would fit with your findings.

Thanks @cathyandclare, yes, that was what I was wondering.

I found it really interesting with DS. I did a LFT on him on the first day when he was really barely symptomatic. I picked up on the virus very quickly because he gets a very unusual cough with it, which I recognised immediately from last year.

On Saturday, he literally coughed once, and I immediately took his temperature and it was 37.7. At that point the LFT test produced the faintest of faint lines, but it was a definite positive.

The following day he was very clearly symptomatic and the LFT produced a strong line after 2 minutes.

I just find it so interesting that DH is so symptomatic now and shows nothing on the LFT, bearing in mind that he is double vaccinated.

No PCR test results yet obv for me and DH but hopefully in a few days. We did it by post and just posted them a couple of hours ago, so there will be a wait of a few days.

You are your husband could have Covid or you could have another bug/ virus.

There is so much going around at the moment. It’s not just Covid.

Did you test positive in March last year?

No guarantee that you have Covid. Lots of other acute respiratory viruses around. LFT will have a sensitivity limit like an ELISA, may only detect as positive if concentration is in micrograms and not nanograms, therefore if viral load is higher then you’ll test positive.

I did read on here someone was told by a nurse that LFT’s were okay for picking up someone actively contagious. No idea if there is any truth in that but it would fit with the idea of lower viral loads.

I’m also interested to know how you’re so sure you all had covid in March 2020? Were you in hospital to access tests or did you all have antibody tests later on?

[quote Pantene23]www.qmul.ac.uk/media/news/2021/smd/lateral-flow-tests-are-95-effective-at-detecting-covid-19-when-used-at-the-onset-of-symptoms.html[/quote]
Reposting, as I saw this the other day when looking up the LFT aren’t reliable/only50% effective etc I keep reading here.

DS has just finished his isolation as have DH and I after DS tested positive on LFT, then PCR. He had been testing every day for a while as DH is on chemo, and is the ‘weakest link’.

All of us are double vaccinated, DS had no symptoms before and only minimal after. Hospital happy to have negative LFT tests from us for DH to have chemo.

Antigen testing is notoriously unreliable, you need to test on the day of the highest viral load to get a true negative/positive usually day 3 or 4. Equally not doing it correctly, using an incorrect swab or even swabbing the mouth instead of the nose can create a false reading as can getting the swab to buffer timings wrong.
Good luck I hope you all feel better soon

I am double vaccinated (Pfizer) and have covid ATM
I was part of a study doing daily testing so my tests were like this:

Day1 - LFT negative, PCR positive (didn't know PCR result at that point obviously) - asymptomatic
Day 2 - LFT very faint positive, PCR positive - first symptoms headache, chills
Day 3 - LFT decent positive
Day 4- LFT negative (but symptoms ongoing)
Day 5 - LFT negative (but symptoms ongoing)

Currently on day 6, have sinus pain, sneezing and coughing. But LFT presumably would be negative.

Maybe you missed the testing positive window. Did you do a PCR?

@Harp1977

Antigen testing is notoriously unreliable, you need to test on the day of the highest viral load to get a true negative/positive usually day 3 or 4. Equally not doing it correctly, using an incorrect swab or even swabbing the mouth instead of the nose can create a false reading as can getting the swab to buffer timings wrong. Good luck I hope you all feel better soon

Thanks @Harp1977 that does make a lot of sense.

Swabbing technique is a major factor in LFT false negatives.

Is your DS secondary age, and has he done bi-weekly tests since the schools went back (with early ones under supervision)?

Whatever you've got, I hope you feel better soon

@AvaCallanach

I am double vaccinated (Pfizer) and have covid ATM I was part of a study doing daily testing so my tests were like this:

Day1 - LFT negative, PCR positive (didn't know PCR result at that point obviously) - asymptomatic
Day 2 - LFT very faint positive, PCR positive - first symptoms headache, chills
Day 3 - LFT decent positive
Day 4- LFT negative (but symptoms ongoing)
Day 5 - LFT negative (but symptoms ongoing)

Currently on day 6, have sinus pain, sneezing and coughing. But LFT presumably would be negative.

Maybe you missed the testing positive window. Did you do a PCR?

@AvaCallanach yes that does make sense. Thanks. We've just done a PCR test.

I'll not comment on how we know that it was covid last year, as it's not central to the thread, but it was very clear at the time.

For this time, it's also very clear that we caught it from DS because of our lifestyle and that lack of any other variables that could have led to the symptoms that we have. The PCR tests will clear it up definitively in time, I'm sure.

Maybe we should keep trying the LFT each day just to see. Interesting!

@UnmentionedElephantDildo

I did wonder about swabbing technique. I don't feel very confident about my own tbh and less so about DS. It did seem to work a treat on Saturday though. I'll go and read the book again.

Ds is primary age and hasn't been doing bi-weekly LFTs. (sorry)

Hi,

Just to complete the dataset on this thread, my PCR test came back positive.

DH did two tests in the end and both were negative. This is in spite of his having clear covid sypmtoms, and having never been anywhere else to catch anything else other than covid at home from DS. DH started symptoms on the same day as me, two days after DS.

That implies to me that with his two vaccinations, not only could he not produce a postive LFT, he also couldn't produce a positive PCR, even while heavily symptomatic for a full week. That is pretty interesting.

I don't know anything scientifically but can contribute anecdata.

My work colleagues 15 year old son 'felt a bit ill' so tested himslf. Positive LFT.

She also felt a bit off and tested herself. Negative LFT.

Her husband felt fine, but tested. Negative LFT.

All took PCRs.

The following morning, having had a night of flu like symptoms, my colleague tested herself again. Negative LFT.

All three PCRs positive.

The dad is double vaxed - just. The mum would have been double vaxed the day after testing positive.

Both mum and son continue, three days in, to have mild symptoms. The dad continues to have none so far.

Thanks @Scarby9. It definitely takes some careful thought to interpret it all doesn't it?

I hope your friends feel better soon. Xx