Weird lateral flow results

[Tootiredforallthis]

Just wondering if anybody else has experienced this or has some kind of explanation.

In July (3 weeks after my second jab) my DD tested positive for Covid. At the time I started getting symptoms and got a faint line on LFT but PCR was negative.

Since then I have done a lot of LFTs (for work). Every single one has been negative after 30 minutes but then has shown a faint line if I look at it again after a few hours.

I'm not particularly worried but I am curious as to why it is happening. I know lots of people doing regular LFTs and nobody else has had this happen.

Never had this.
I leave my lateral flows on my bedside table and in the morning they are still negative.
How strange.

I expect you were actually positive in July, but had a false negative PCR (they miss around 1/5 cases). You can test positive in LFT for weeks afterwards (not supposed to test again for 90 days for this reason), so I think you are still testing weakly positive after having COVID in July.

One of my sons seem to always get a line but always after the 30 minutes, and it becomes really obvious after about 2 to 3 hours as it dries out. I do think if you overload the test with sample, it can create a line, maybe like an evap? We didn't read the instructions properly and were emptying the entire sample into the test when you're meant to do just 2 drops. However it's almost always my 13 year old who gets a line after the 30 mins, but never before!

My old style LFT showed faint positive after the 30 minute time several times over a few months. I've since had a Covid blood antibody test through Zoe (which looks for infection antibodies specifically, not vaccination ones). The antibody test was negative, so I think it's just that certainly the old tests could show a faint line if left for ages. We've got a new type of LFT in our most recent boxes and those haven't done it yet, so maybe it's test type specific?

This happens to one of my DCs and has done on every lft since March. It shows negative until the 30 minute mark then a faint line appears. On the old style if he only swabs his tonsils it stays negative but from his nose it brings up the second line it's a mystery! He has recently had covid and the second line on his actual positive lft was definitely darker and came up straight away.

@Tootiredforallthis I didn't realise until recently that this is why you must only look at 30 mins as you can get false positives if you look later

It does say this in the booklet but I missed it initially 🤦🏼‍♀️

Glad to find it's not just me. I knew not to take notice of the result after 30 minutes but once I'd seen it happen I was curious so now I do keep them just to see.

It could be that I've overloaded the sample, as I do tend to put most of the liquid on, but I also do the same for my DCs' tests so not sure.

We've just got a supply of a different type of LFTs at work so it'll be interesting to see if they do the same thing.

@Watsername That was what I was thinking but it's outside the 90 days now so I had started to wonder if there was another reason.