How reliable are positive lateral flow?

[ThistlesAndUnicorns]

I had a faint positive yesterday morning then a strong positive last night. Everyone else is testing negative. I've been trying to find out how reliable they are but keep getting contradicting advice so wondered about others experiences? I sent away a PCR today.

Very - the difference in the strength of the positive line is an indicator that you were more infectious this morning than yesterday. DP had Covid over New Year. He self-isolated as soon as he tested faintly positive on a lft and I never caught it.

Sorry - should have put "more infectious yesterday evening than yesterday morning".

Very. You don't need a PCR anymore. If the LFT is positive you report and isolate .

I had a very faint one almost like an evap line to begin with.

This probably answers you question at least 99.9% specificity though maybe as high as 99.96%. Specificity relates to how accurate a positive test is. This is very accurate for these rapid tests a lot them used for other diseases are 95% specificity.

You can sometimes get false negatives but not false positives, I'm afraid.

@TigerLilyTail

You can sometimes get false negatives but not false positives, I'm afraid.

Not true - these boards are full of people getting false positives (later confirmed negative with PCR), especially with the FlowFlex brand.

Thank you everyone! We all isolated straight away. Has anyone had a positive ltf but negative PCR? This happened to a friend of mine but I'm not sure how common it is.

I’ve heard of false negatives but yet to hear of a false positive from a LFT

My husband got a negative PCR and a positive LFT the next day

@ThistlesAndUnicorns

Thank you everyone! We all isolated straight away. Has anyone had a positive ltf but negative PCR? This happened to a friend of mine but I'm not sure how common it is.

I have had multiple positive LFTs and negtive PCRs over many months. But I have never had any symptoms.

The only person I know who had a false positive lft it was a single false positive and all the rest of lfts taken were negative. Lfts that get stronger and are all positive mean you have covid definitely

Very reliable if positive reault. But they sometimes miss cases so a false negative.

I think they are very reliable. All of our positives were picked up very clearly by LFT.

I've had a few 'positive' LFTs but they were evap lines really just like those false faint positives you get on pregnancy tests. A positive LFT will get stronger very quickly - I had a positive PCR yesterday, negative LFT this morning and strong positive LFT tonight.

They've been reliable for us. Detected both mine and my sons covid the day before symptoms started.

@sageandbasil

My husband got a negative PCR and a positive LFT the next day

That’s potentially OK — he might not have been infectious when he did the PCR, and it developed overnight. Did he do any lateral flows before the PCR?

@SmellyOldOwls

I've had a few 'positive' LFTs but they were evap lines really just like those false faint positives you get on pregnancy tests. A positive LFT will get stronger very quickly - I had a positive PCR yesterday, negative LFT this morning and strong positive LFT tonight.

What you have to remember is that a lft shows whether you are infectious. DP's positive didn't get stronger quickly: it was identical and faint twelve hours later because he picked up on his symptoms being Covid early on.

With lfts it's possible to get something faint then even 5 or 6 hours later/the next morning, a strong line, although it's not guaranteed. Based on the experience of 3 people in the house going through Covid around 5 days apart from the first positive, I suspect the first appearance of the lines indicates the peak infectious stage. I was not at home for a couple of days, and testing negative, when the positive appeared back home. The other person who was with them for that time was the next to get the positive, I tested inconclusive on PCR 5 days later than that, but got the lft result a day or 2 later.