Why do some people keep getting false positive LFTs?

[Watsername]

DS(17) tested positive on a LFT yesterday - received negative PCR result today. He is completely well, no symptoms of any sort.

This has happened twice for him before (two weeks apart in August).

Each time has been from a different box. The last one was FlowFlex, as opposed to the previous nose AND tonsil kind. I have watched him do each one. All 3 have been in the morning - may be relevant?

Does anyone have any theories as to why some people seem to be prone to testing false positive on LFTs?

Silly q maybe but did he have anything to eat or drink beforehand?

I'm wondering whether it's acid reflux. I think acidic drinks tend to give false positives to 'trick' the test, and I'm wondering if morning reflux could do the same. I started a thread a day or so ago about what I'm pretty sure is a false positive, it was really strongly positive but the PCR and further LF tests have been negative. The positive one was the only one I've done first thing in the morning. I feel absolutely terrible though, so I do have symptoms, but I expect it's one of the many other available viruses at this time of year.

Maybe it's a false negative PCR?
Just sayin....

Are you sure it's not the PCR that is wrong

The only other thing I can think of, and I'm probably being bonkers, is that I somehow had it in my nose and then fought it off 😆 I had definitely had quite a long exposure to someone with Covid a couple of days before so I wondered if it was there but the infection didn't take hold. I think that's the dose of night nurse talking 😆

I have had this twice so far and waiting for a third PCR result now.
I had a positive LFD and negative PCR whilst looking after my 2 year old with Covid. The LFD seemed most likely accurate. I was shocked about the PCR.
Mine have all been in the nose only LFD but the most recent one was 9pm last night and I hadn’t had anything to eat or drink since 6pm. So we will see what the latest verdict is.
I have very slight cold symptoms but no official symptoms.

Each time it’s been first thing in the morning before eating or drinking. (All the hundreds of evening ones he does for school have been negative).

No symptoms at all. Not a known close contact.

I suppose it’s possible the PCR was wrong this time and we’ve tested too early. But it’s just like the previous two times.

Just been googling...I wonder if mucous could be his issue?

inews.co.uk/news/politics/lateral-flow-tests-positive-covid-test-results-unreliable-caused-snotty-noses-1245117

Its not coloured snot, but the clear liquid comes out thicker from the tube than it does for anyone else in the family when you drop it onto the test.

I had 4 positive lft, followed by 2 unreadable pcr followed by 2 negative pcr. I came to the conclusion I had covid but by the time I got the positive lft and unreadable pcr it was heading out of my system. I've isolated anyway but it doesn't leave me very confident in testing.