Faint positive LFT within seconds, changing to negative at 15+ minutes?!

[GH5385]

Our household all has confirmed Covid and we’ve been isolating at home. I tested my youngest today and it turned a faint positive almost straight away, then when I went back after 15 mins it was completely negative, still negative at 30 mins. Did another test from a different box and the same thing happened. Any ideas what it means?

She hasn’t had any symptoms apart from tiredness and preschool said she ‘wasn’t herself’ last week. T lines have always been faint for her but definitely there at 15/30 mins.

Some of the tests we have used you can almost see the line moving up the strip - like it starts right at the bottom, and ends up at the 'control' window. Is that what's happened do you think? It says to read them at 15 minutes so I'd assume you're fine.

You're not meant to read them early, I assume this is why. Though with all our once the positive line appears ( often way before 15minutes) it stays!

I've known pregnancy tests do this, for a minute or so as the liquid is moving up the strip it looks positive, then it slowly fades but it is negative, I assume lateral flows work the same way .

Interesting…I know it says not to read them early but with all the other positive tests various family members have done recently they have all turned positive very quickly then stayed that way.