Will LFT show if I caught covid yesterday?

[AmyD54321]

Hi, hope someone can offer some advice. How soon will a lateral flow test recognise infection? For example, if I take a negative test today, could I have caught it yesterday but it hasn't registered yet? Or does a negative lateral flow mean that up til the moment I take the test, I don't have covid?

Hope that makes sense, and really hope someone can help!

I don't understand the difference between your two statements. All a negative LFT shows is that do not currently have a viral load of COVID that will produce a positive test.

It takes on average 2-14 days to show positive

But if you think you have been in close contact get a PCR test and isolate

How can the test know you've got Covid before you've taken it? A lack of a test doesn't prove a lack of the virus?

However the virus has a 10 day incubation period.

If you were in contact with someone with the virus yesterday, you need to isolate for a further 9 days regardless of a LFT result.

I've tested positive yesterday on a PCR but my lateral flow was negative. I think the LFT's aren't accurate enough to detect small amounts of the virus.

The average incubation period is 5 days and LFT only pick up 50 to 70% of cases.

Mine took 2 days

Some LFT are not picking up positive PCR tests at all, maybe just down to viral load not being too great.

LFTs are not for telling you if you have the virus or not. LFTs are for you to take at random, because they'll pick up SOME cases that we wouldn't otherwise know about - and it's more practical to take regular LFTs than regular PCRs. But they aren't very reliable. So if you have any reason to believe you might have Covid, take a proper, reliable PCR test.

DS tested positive on an LFT 5 days after being sent home to isolate. He had tested negative on 2 other LFTs in the days between starting isolation and testing positive.

Yet he must have caught it from the person/a person at school 5 days before as he hadn’t seen anyone in the intervening period.

So to answer your question, it can be incubating in you for a few days before an LFT picks it up.

If seems to vary from person to person.

My niece probably caught Covid on a Sunday. She had a sore throat from Tuesday, but kept testing negative on LFT until Friday.

My niece was the same @NotThisWeekSatan. Her year group were sent home to isolate after school on Monday. Symptom (sore throat) started on Tuesday, but still testing negative until Friday. Same thing for other kids who were asymptomatic.

Armagony it’s odd isn’t it? (And also annoying, as if he’d had symptoms initially we would be out of isolation by now, but with no symptoms they go from the date of the positive PCR !)

If you mean will the test know you came into contact with an infectious person and have now picked up the virus, then no. This is why the self isolation period is set as 10 days because the virus has an incubation period of anywhere up to (and over, in some cases) 10 days. So there is always a point at which you first start testing positive if you do have the virus but testing negative today is not proof that you won't have caught the virus, if that makes sense.

@NightmareLoon

I don't understand the difference between your two statements. All a negative LFT shows is that do not currently have a viral load of COVID that will produce a positive test.

@NightmareLoon Id go one step further and say that it doesnt even mean that. It means that there is not a recognisable virus sample on the swab. The person could still have a viral load but for whatever reason the swab hasn't picked it up.

@AmyD54321 No. It doesnt. Lateral flow only pick up about 60% of positives. They are not accurate enough for diagnosing or ruling in/out.

Thanks everyone, that makes perfect sense. I came into close contact with a positive person at the start of the week so I’m isolating, of course, but now just waiting to see whether I develop any symptoms! Negative LFT all week so far. Would it be worth doing a PCR too?

I would do a PCR for peace of mind

A negative test result could still mean that you have caught covid, but are still "brewing" it.

I think by day 5 or 6, a negative PCR would be quite reassuring although obviously you have to complete your isolation. Someone on here said Delta shows up more quickly than previous variants, but I haven’t read that anywhere else yet.

That's how it happened with us. My children spend the night at their grandparents at the weekend. When we went to pick them up grandpa had just done lateral flow which was positive, booked a drive through PCR which confirmed it. Monday all four of us took pcr tests. One child was positive, the rest negative. I then did a lateral flow which was negative. Retook PCR test a day later and 3 out of 4 of us were then positive. My lateral flow still negative.

@NotThisWeekSatan

Armagony it’s odd isn’t it? (And also annoying, as if he’d had symptoms initially we would be out of isolation by now, but with no symptoms they go from the date of the positive PCR !)

Yes. My niece's friend caught it at the same place, but didn't show symptoms, so had to isolate for longer than my niece as it went on the PCR test day instead 😬

The delta variant tends to show sooner than previous variants. Hopefully you haven’t caught it.

@SunbathingDragon
Have found this article backing this up:
www.nature.com/articles/d41586-021-01986-w

Lateral flows are not accurate - we recently went on holiday with some people who did multiple lateral flows all negative, now we all have covid and they have tested on PCR as positive as well.