Negative PCR after positive lateral flow

[IDoAllMyOwnStunts]

So myself and DH went to community testing site in our town on Sunday. No symptoms at all.

(I wanted to meet my dad for a walk and wanted to check I was clear.).

We both had the lateral flow test. I get a text half an hour later - negative. DH gets a text to say he's positive.

Test and trace rang - told us we both had to isolate for 10 days. Fair do's.

The following day DH had a PCR test which has come back negative. Still both have no symptoms.

Not much online about what we do now. Whether to still isolate. I'm thinking yes?

@Theunamedcat

Have they had covid in the last 90 days? Lft will still show positive if they have

Have you got a source for that claim, because it's rather unlikely!

A PCR test can show +ve's for a while after infection, although to a far lesser degree than is sometimes suggested by those attempting to discredit the test. As a result though they suggest that PCR tests should not be repeated within 90 days of a +ve test as the results would be suspect.

LF tests though are much less sensitive.

The school have told the children if they have had covid in the last 90 days they cannot take the lft test 🤷‍♂️

@Theunamedcat

The school have told the children if they have had covid in the last 90 days they cannot take the lft test 🤷‍♂️

This is probably because if you've had covid, you're HIGHLY unlikely to catch it again within a 90 day period!

Everyone is at risk of getting a false +ve from both an LF or a PCR - generally with PCR's the fact you also have symptoms tend to reduce the risk of a false +ve. Because LF's are used on everyone, the chance of a false +ve is greater, roughly 1 in 1000. I guess excluding people who couldn't possibly be genuinely +ve, helps reduce these numbers.

generally with PCR's the fact you also have symptoms tend to reduce the risk of a false +ve

That's not strictly correct. It's that because the LFT is done on everyone the number of false positives relative to the number of actual positives becomes significant. So e.g., if the false positive rate is 1 in 1000 but the number of people who have Covid is 2 in 1000 then 1/3 of people who get a positive test result don't have Covid. Which when you are asking people to not go to school or work for 10 days is problematic.

@JaninaDuszejko

generally with PCR's the fact you also have symptoms tend to reduce the risk of a false +ve

That's not strictly correct. It's that because the LFT is done on everyone the number of false positives relative to the number of actual positives becomes significant. So e.g., if the false positive rate is 1 in 1000 but the number of people who have Covid is 2 in 1000 then 1/3 of people who get a positive test result don't have Covid. Which when you are asking people to not go to school or work for 10 days is problematic.

That's exactly what I said, but in fewer words.

If you have symptoms, your chances of having covid are a lot greater to start with.

OP I suggest your partner contact the GP for confirmation.

For NHS staff - if we get a positive LFT we need to get a PCR test. If that is negative we return to work.

We have had a few positive LFTs followed by negative PCR. That happened to one person 3 times. I don't know what happened with them. We are advised not to do LFT within 90 days of a positive PCR. This is because there is a risk of false positive.

I suspect (although I don't know for sure) that many false positives are people who have had Covid without realising.

Although the risk for a false positive with an LFT is 1/1000 (0.1%) the risk of a false negative with a PCR is up to 50%, especially if asymptomatic.

I know the “rules” say you can return to work/school after the PCR overrules it but, as a teacher, that makes me nervous.