Lateral Flow ......how reliable ???

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I've known of a few cases where the test said Negative but PCR  was Positive
4 people I know working in same shop all had very nasty cold .......logic said Maybe Covid
All 4 took lateral flows 3 times over 3 days with Neg result
All went for PCR ...........All positive 
Of course ,we know lateral flow is not 100 % but it's quite worrying just how innaccurate it can be ....must be lots of people walking around thinking negative but spreading the virus
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  • RolandRoland Frets: 6228
    The biggest variable is not the test itself, but how well people take their sample.
    Known here as Old Misery Guts or the Big Bad Classified's Sheriff. Also guitarist with  https://www.undercoversband.com/.
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  • CirrusCirrus Frets: 6850
    edited December 2021
    Yeah, I'm curious about this too - I've not seen any particularly credible reliability figures from a source I'd trust, but I've heard everything from "they only pick up 20% of positives" to "they're very very accurate if you're actually infectious when you do one."

    I think there's an element of corporate & personal liability in how their use is being mandated - basically, however ineffective they are, they're the only tool available short of doing PCR tests every day which would be way too disruptive. If you mandate their use in your organisation, or take one before going out in public, at least you can say you did your best to be responsible.
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  • munckeemunckee Frets: 8707
    I believe they are effective before symptoms develop but much less so once symptoms develop. 
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  • chris78chris78 Frets: 5934
    Purely anecdotal, but a friend of my daughter had a positive lateral flow and then a negative PCR. Another had a negative lateral flow and positive PCR. Neither had symptoms.
    Obvious answer to me is only to test people who are actually ill
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  • CHRISB50CHRISB50 Frets: 2873
    We’ve been doing LFT’s every couple of days as normal.  

    My 2 kids and I have all had colds the last 7-10 days. Wife fine. 

    Youngest tested +ve this morning on a LFT. The rest of us -ve. She’s just been for a PCR so I guess we’ll find out if the LFT was accurate. 

    I’ve also ordered PCRs for the rest of us. 

    I’ll update once we get the PCR results. 

    I can't help about the shape I'm in, I can't sing I ain't pretty and my legs are thin

    But don't ask me what I think of you, I might not give the answer that you want me to

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  • munckee said:
    I believe they are effective before symptoms develop but much less so once symptoms develop. 
    I think this is a fairly accurate statement - my band all had negative LFD tests, but we'd all started to show (very mild) symptoms by the time we took them. All of us ended up with positive PCR tests.
    <space for hire>
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  • axisusaxisus Frets: 21823
    Some info from the Pharmceutical Journal back in May:

    https://pharmaceutical-journal.com/article/feature/how-reliable-are-lateral-flow-covid-19-tests

    Cochrane review, published on 24 March 2021, investigated whether commercially available, rapid point‐of‐care antigen (lateral flow) and molecular tests were accurate enough to diagnose COVID‐19 infection reliably, and to find out if accuracy differed in people with and without symptoms. 

    The reviewers included 64 studies published up to September 2020, which investigated 16 different antigen tests and five different molecular tests.  

    They found that in people with confirmed COVID‐19, antigen tests correctly identified COVID‐19 infection in an average of 72% (ranging from 34% to 88%) of people with symptoms, compared with 58% of people without symptoms. In addition, they found that the tests were most accurate when used in the first week after symptoms developed. 

    In people who did not have COVID‐19, antigen tests correctly ruled out infection in 99.5% of people with COVID-19-like symptoms and 98.9% of people without symptoms. 

    Although the overall results for diagnosing and ruling out COVID-19 were good, the reviewers pointed out that 69% of studies used the test in laboratories instead of at the point of care.  

    They concluded that some lateral flow antigen tests may be most useful to identify outbreaks, or to select people with symptoms for further testing with PCR, allowing self‐isolation or contact tracing, and reducing the burden on laboratory services. But they added that more evidence was needed on rapid testing in people without symptoms.  

    Analysis of community testing data, released by the Department of Health and Social Care (DHSC) in March 2021, suggested that lateral flow tests had a specificity of “at least 99.9%”. Specificity is a measure of how good the test is at detecting true negative cases; in this case, a 99.9% specificity means that there is fewer than one false positive in every 1,000 lateral flow tests carried out.  

    However, the analysis used data from locations using the supervised testing model.  

    Clinical evaluation carried out by Public Health England (PHE) and the University of Oxford at the end of 2020 showed that lateral flow tests were accurate enough to be used in the community, including for asymptomatic people, but that the tests performed best when levels of virus are at their highest and people are in the most infectious stage of the disease. 

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  • My daughter is a molecular biologist. She's told me that Lateral Flow Tests need you to have a reasonably decent viral load in order to be Positive. PCR Tests are more sensitive, which is why people can have a Negative Lateral Flow Test at the same time as having a Positive PCR Test.

     Lateral Flow Tests are much quicker and simpler to do. Obviously there's going to be a question of how well the sample was taken in the first place, especially in relation to self administered sampling, given that most people do not spend their lives sticking sample swabs in themselves.
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  • GrunfeldGrunfeld Frets: 3684
    I wonder how the LAMP tests compare?  You provide a sample of saliva.
    These tests replaced the Lateral Flow Tests at the hospital I work at.  I've no idea how popular the test is, let alone its sensitivity and specificity.  From a user's perspective it's easier to spit in a thing compared to sticking a swab in my face. 

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  • NelsonPNelsonP Frets: 2376
    False positive rate is low, c.1 in 1000
    False negative rate is high, c. 50%

    So they are a fairly crap way to ensure that you haven't got covid and it's a bit meaningless to set it as a requirement for nightclub entry. Although it is better than nothing.
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  • I've only had negative tests even when I thought I had a strong chance of being positive. I just don't know that I'm doing the sample properly. I mean, I always gag and I always end up sneezing because of the tickle up my nostril. But it's not obvious if there's a specific way to get a good sample.
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  • YorkieYorkie Frets: 167
    munckee said:
    I believe they are effective before symptoms develop but much less so once symptoms develop. 
    Wife and son had COVID-19 and took daily LFD tests while they had it. Wife was symptomatic, son was asymptomatic. Same results on LFD: faint T line on day one, strong T lines for four days, faint T line on day 6, nothing on day 7. Wife's worst symptoms lasted until day 4, sense of small and taste sadly still gone. In the meantime, daughter and I didn't catch it: 7 negative LFD, 2 negative PCR. Go figure. 

    Regarding getting good samples, don't worry too much. A more infective and transmissible virus variant means you can now basically touch your nostrils a bit and test positive. My son (4yo) did the tests himself.

    Jon
    Adopted northerner with Asperger syndrome. I sometimes struggle with empathy and sarcasm – please bear with me.   
    My trading feedback: https://www.thefretboard.co.uk/discussion/210335/yorkie

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  • crunchmancrunchman Frets: 8368
    NelsonP said:
    False positive rate is low, c.1 in 1000
    False negative rate is high, c. 50%

    So they are a fairly crap way to ensure that you haven't got covid and it's a bit meaningless to set it as a requirement for nightclub entry. Although it is better than nothing.

    They are utterly useless for that, as they are self reporting.  As far as I know you can just upload the serial number of the test kit to the government website and say it was negative.

    They have some use if use properly and the results are reported in good faith, but using them for Covid passports is an utter waste of time.
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  • CHRISB50CHRISB50 Frets: 2873
    CHRISB50 said:
    We’ve been doing LFT’s every couple of days as normal.  

    My 2 kids and I have all had colds the last 7-10 days. Wife fine. 

    Youngest tested +ve this morning on a LFT. The rest of us -ve. She’s just been for a PCR so I guess we’ll find out if the LFT was accurate. 

    I’ve also ordered PCRs for the rest of us. 

    I’ll update once we get the PCR results. 
    Her PCR came back positive. 

    My first PCR came back as inconclusive. 2nd one came back negative. Other daughter and wife all also negative. 

    So far in our own experience, the results of the LFT and PCR are the same. 

    I can't help about the shape I'm in, I can't sing I ain't pretty and my legs are thin

    But don't ask me what I think of you, I might not give the answer that you want me to

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  • crunchman said:
    NelsonP said:
    False positive rate is low, c.1 in 1000
    False negative rate is high, c. 50%

    So they are a fairly crap way to ensure that you haven't got covid and it's a bit meaningless to set it as a requirement for nightclub entry. Although it is better than nothing.

    They are utterly useless for that, as they are self reporting.  As far as I know you can just upload the serial number of the test kit to the government website and say it was negative.

    They have some use if use properly and the results are reported in good faith, but using them for Covid passports is an utter waste of time.
    Hard to argue against that. Self reporting is merely us (as citizens) helping the government capture data, that's all. I've done a few LF tests and popped onto the website to file the results, but it's totally an honour-based system. And that assumes you actually do get the swab into those little places it needs to go. The tonsils swab makes me gag - so I hope I'm getting it right. 

    Slight aside: I've been to a few gigs that needed some form of proof you're clear. They can scan QR codes on tickets, but I've never had my Covid passport screen scanned or had it checked that it actually was for me. I've even shown a photo of the QR code when the cell network around the venue was overloaded. 

    I think they're just paying lip service to the idea, TBH. 
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  • CirrusCirrus Frets: 6850
    @TheBigDipper when me and the wife went to get mandatory PCR tests ahead of a hospital stay, I was dreading gagging as someone else administered the test.

    She didn't go that far back. I felt the swab tickling my tonsils, but not far back enough to even be uncomfortable. I said "wait, was that far enough in?"

    The nurse said yeah, people go too far back when they do them at home like they're trying to get the back of their throat - you only need to swab the front of the tonsils where bacteria etc collects, and that's not as far back as people assume. So now I know that, the worst part of the LFT is going deep into the nostril.
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  • Having seen someone "take a lat flow test", I'd say I agree that the test is accurate but the human brain running that particular test might not be.
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  • BlaendulaisBlaendulais Frets: 2400
    edited December 2021
    The trouble with diagnostic tests is people are confused by the language used in test reporting. Terms such as sensitivity accuracy dont mean what a lay person would think they mean.  

    If its positive you have it to all intents and purposes

    https://pubmed.ncbi.nlm.nih.gov/34407759/




    The sensitivity is between 38.32-99.19% BUT YOU CANT SAY that the false negative rate is 1-the sensitivity here as it depends on the population prevalence. if the prevalence is 1% then the false negative rate is very low.  If everyone in the population had covid then yes the false negative rate is 50%

    Thats the problem with diagnostic tests.  Thats why the public health physicians, who are expert at such issues are using it.

    We on the fretboard remain armchair experts at best. At worse we are ignorant and i include myself =)

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  • LAMP testing is pretty accurate apparantly. Been using them for a while. 
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  • YorkieYorkie Frets: 167
    I’ll say it again in case someone has missed it: 

    Lateral flow tests detect nucleocapsid antigens in ANTERIOR NASAL SWABS (read the box if you don’t trust me). Leave your poor tonsils alone. 

    Jon
    Adopted northerner with Asperger syndrome. I sometimes struggle with empathy and sarcasm – please bear with me.   
    My trading feedback: https://www.thefretboard.co.uk/discussion/210335/yorkie

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