Lateral flow tests are just not reliable...

[MariaAngustias]

Started feeling slightly unwell 6 days ago - just bit achey, headache, sore throat. Did daily laterals and all negative. 3 days ago felt quite ill, went to bed, high fever, sore throat, cough... lateral flows still negative. Yesterday did 2 lateral flows both negative, sent PCR off 3 days ago still no result. Today did lateral which lit up positive straight away.
So - is it normal that these tests lag days and days behind before they test positive? I am triple vaccinated btw - does this make any difference in the lateral flow showing a positive. Thank God I am vaccinated cos I feel like death warmed up. Would be interested in hearing others experience of the lateral flow tests x

67% when asymptomatic, 75% when symptomatic, according to an article on the Zoe app.

Symptoms - PCR
Asymptomatic testing - LFT

Was what I thought.

Hope you’re better soon.

DH's LFTs did not show positive until he was about four days into covid. They have gone negative fairly quickly as well, about day 7.

lateral flows are not for symptomatic testing,.

They identified DD had covid on a routine test (confirmed by PCR the following day). Very clear line.

People's experience of them seem to vary widely, though.

Lateral flows work on symptomatic Covid. There’s been a misinterpretation of guidance not to use them when you have symptoms.

LFT aren’t super sensitive so you have to be shedding a lot of the virus to test positive (according to Dr Sarah Jarvis on Radio 2) which is why, if you have symptoms, you should always PCR instead of LFT because lab testing picks up lower levels. I guess that’s why they now say after 7 days if you are negative on LFT then you can stop isolating as you are unlikely to be shedding enough virus to be contagious.

Have you been swabbing your throat as well as nose? Anecdotally (Twitter) the nose-only ones are more accurate if you do actually swab your throat.

I know a few people now who were negative on LFT but positive on PCR who only tested because they were close contacts.

Husband positive LFT negative PCR !

Well I must be some sort of weirdo because I have now had 3 positive LFT tests and 2 negative PCR test.

This is my most recent LFT result, looks positive to me. PCR result just received as negative...

I’ve had the same - 4 days of positive LFT, 2 negative PCR. Very strange.

@Reallybadidea I just did the nose because I had the NHS lateral flows with the short swab that are just for nose.
@Carriemac I did a PCR as soon as I had symptoms according to NHS website cos, up until then, just had vague 'unwell cold type sx'. Maybe I should have had PCR sooner....

We've also had 2 positive lft followed by negative pcr!

[quote MariaAngustias]@Reallybadidea I just did the nose because I had the NHS lateral flows with the short swab that are just for nose.
@Carriemac I did a PCR as soon as I had symptoms according to NHS website cos, up until then, just had vague 'unwell cold type sx'. Maybe I should have had PCR sooner....[/quote]
Yeah, they seem to pick up covid more easily by doing the throat too. The swabs are short but it's perfectly possible to swab your throat with them.

Lateral flow is actually far more likely to work properly when you have symptoms because of the high viral load. MN needs to stop peddling the myth that lateral flow tests somehow know when you get symptoms & stop working. They detect virus, and most of the time if virus is there you will get a positive. However they are not infallible which is why PCR is recommended when you have symptoms & really need to know.

The attached diagram explains how LFT and PCR vary in being able to return a positive result.

Original file: media-exp1.licdn.com/dms/image/C4D22AQG4bAY-AUB6Hg/feedshare-shrink_800/0/1640036988215?e=1643241600&v=beta&t=mc5o0ETcRBrG3ldJlgtg3sfQ-Cko310Crn3K3cS_4-c

New guidelines are to use LFTs on day 7

Those with symptoms and active covid will be encouraged to use the lft to release. They’ll test negative and as long as they don’t have a fever they’re safe to carry on with life.

They will still have the other symptoms so this don’t use lft on symptomatic covid is bollox

@Palavah

67% when asymptomatic, 75% when symptomatic, according to an article on the Zoe app.

The Guardian reported... A recent paper demonstrated that LFTs, when used correctly, are likely to have a sensitivity above 80% and in many cases above 90%.

I guess the key words are when used properly.

@Carriemac

lateral flows are not for symptomatic testing,.

LFTs are distributed for that purpose - that doesn't mean they don't work if you have symptoms.

Continuing to LFT while waiting for PCR results is sensible.

@Carriemac

lateral flows are not for symptomatic testing,.

Some of them are, it depends which ones you get.

I read on Twitter this morning that they are more reliable if you swab both nostrils and throat. The newer ones we have (which you can use when symptomatic, it says on the box) are supposedly only for nostrils.

I've done lft every day for past week, sometimes twice a day. All negative. I started with a cough Xmas night. Still negative. A friend who I'd spent time with Xmas Eve tested positive on lft Boxing day so I took a pcr. Positive. I feel really ill but still showing neg on lft. My friend is asymptomatic but strong positive on lft.

67% when asymptomatic, 75% when symptomatic, according to an article on the Zoe app.
Shout it from the rooftops! I'm so sick of people thinking LFTs "don't work" if you have symptoms. They have a fairly high false negative rate, regardless of symptoms so you shouldn't trust them if you have any reason to suspect you might have it. For those who like their evidence anecdotal MiL got four negatives in the 24 hours between taking her PCR swab and getting the result - which was positive. She's a nurse, so fairly likely to be swabbing correctly.