How are you guys getting on with Lateral Flow tests?

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  • jpfampsjpfamps Frets: 2637
    thebreeze said:
    So the US are saying they're useless and should be thrown in the bin.  There have been question marks about PCR tests and the cycles since the beginning.  How the hell do they know what's really going on?

    The PCR test is generally regarded as most reliable test for presence of viral genetic information. It is highly specific by design.

    Also how do you think we have identified the C19 variants? By sequencing DNA applified by PCR from viral samples (and before you say that C19 is an RNA virus, the PCR test uses viral RNA as a templiate to generate DNA).

    PCR is well established technology and is used for many other viruses; it is regarded as the gold standard for HIV for example.
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  • jonnyburgojonnyburgo Frets: 9280
    We have them through work, about 5 positives so far in last 6 months
    "OUR TOSSPOT"
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  • SnapSnap Frets: 4900
    Cols said:
     It’s a screening tool.

    A lateral flow test will pick up an average of 40% of asymptomatic cases - depending on how expertly the swab is taken. 
    Let's put a bit more on this statement

    Public Health England study - 26 million lateral flow tests over about a month between March and April this year. Out of these there were 30,904 positive results. Of these, about half were checked in a lab with a PCR test. They found that 82% of them were correctly identified as positive. 

    Now you can argue that only using half of the original positive cohort introduces an error step, but it should be representative of the whole 30,904 cohort. So saying a lateral flow is only 40% accurate, isn't right, not by a long shot.
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  • ColsCols Frets: 3727
    Snap said:
    Cols said:
     It’s a screening tool.

    A lateral flow test will pick up an average of 40% of asymptomatic cases - depending on how expertly the swab is taken. 
    Let's put a bit more on this statement

    Public Health England study - 26 million lateral flow tests over about a month between March and April this year. Out of these there were 30,904 positive results. Of these, about half were checked in a lab with a PCR test. They found that 82% of them were correctly identified as positive. 

    Now you can argue that only using half of the original positive cohort introduces an error step, but it should be representative of the whole 30,904 cohort. So saying a lateral flow is only 40% accurate, isn't right, not by a long shot.
    The Cochrane review determined that lateral flow tests detect 57.5% of asymptomatic cases.

    https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD013705.pub2/full

    The problem is that it’s 57.5% referenced against a PCR test.

    The PCR test is exquisitely sensitive once you’ve got some virus in your extraction solution, but the challenges of taking a swab sample mean that it’ll realistically detect 70% of infected cases.  It’s the very best we’ve got, but it’s not perfect.

    https://www.bmj.com/content/372/bmj.n287/rr

    So in reality, the lateral flow test will pick up an average of 40% of asymptomatic cases - depending on how expertly the swab is taken.

    It does better at symptomatic cases - the limitation is that it’s got a much higher limit of detection than the PCR test, so you need more virus on your swab.  And you get that with symptomatic cases.

    Once you’re symptomatic, however, you should be self-isolating and arranging a PCR test.
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  • SnapSnap Frets: 4900
    The facts appear to be these:

    A lateral flow test is a possibly as high as 82% as reliable as a PCR test. You can then overlay a load of other variables, most notably the reliability of self administered test etc, but referencing PHEs latest study, they say a lateral flow test has a 82% overlap in terms of accuracy with a PCR test. 

    It's blindingly obvious that any test will only detect a percentage of in population cases. For a start, not everyone with the infection will be tested, and secondly when a test is done there is always the potential for testing error. You can't test everyone who's asymptomatic, so we won't ever know how many people a lateral flow test could pick up.

    At a given time, it may well be that a lateral flow test will pick up 40% of the asymptomatic cases in a population. However, that is a very different situation to using lateral flow tests in a constrained population, such as those at border control. In this situation, where you would test, say, everyone, you would pick up as many of the asymptomatic cases as is possible as dictated by the accuracy of the testing process. If we say that a lateral flow test will pick up 82% of the cases that a PCR will, then your lateral flow test is pretty damned good, and you will only lose 18% of your positives (vs testing everyone with a PCR test).
    However, you then have the bummer of holding your tested population in isolation til the tests come through. 

    What we can confidently say is that a lateral flow test has a very good comparison in detection terms to a PCR test, but a PCR test is better still. That isn't a surprise though is it?

    lateral flow tests aren't even properly reported - how many people don't report the results, especially if they are negative? We don't know. So we don't know from this route, how many it is or isn't picking up, not at all. We have to guess/aka model. Same thing really. Modelling just purports to be cleverer. Not always the case.

    I don't agree with what you have taken from the Cochrane review at all, either. You appear to be selective in your referencing. There is a lot more to take from that review and the limitations and weaknesses that they state bear consideration as well.

    You are doing it again really I'm afraid - taking figures from various places, quoting the parts that support your gloomy view. 
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  • ColsCols Frets: 3727
    edited June 17
    @snap, if you would be kind enough to provide a link to this PHE study you’re referencing it would be most helpful.  It’s difficult to comment on it otherwise.

    With regard to your statement “that is a very different situation to using lateral flow tests in a constrained population, such as those at border control”, you have a misunderstanding.  Border control do not conduct the tests.  Nor would they want to; could you imagine the chaos at border control with everyone standing around for 30 minutes waiting for their test to develop?

    You need to present a negative test result before travelling.  If you cannot, you’re denied boarding.
      
    I don't agree with what you have taken from the Cochrane review at all, either. You appear to be selective in your referencing. There is a lot more to take from that review and the limitations and weaknesses that they state bear consideration as well.”

    If you could provide a bit more detail on where you don’t agree and why, it would be appreciated.  Simply saying “I don’t agree” doesn’t actually move the debate along.

    You are doing it again really I'm afraid - taking figures from various places, quoting the parts that support your gloomy view. 
    I’ve taken data from two peer-reviewed papers and demonstrated the limitations of the lateral flow test.

    Don’t get me wrong; I’m not trashing it.  It has a number of great advantages; it’s cheap, fast, can be executed by minimally trained personnel and you don’t need expensive laboratory equipment.  You’re also unlikely to get false positives.

    That’s why it’s great as a mass screening tool and a warning indicator.  What it can’t do is provide reliable assurance that someone isn’t actually infected, such as you might want for international arrivals.
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  • SnapSnap Frets: 4900
    Big sigh @Cols. Mate, I know how testing works in and out of countries.

    I was trying to make the point that if you have a controlled population where you can test everyone you will get a true picture of testing efficiency. It's impossible in the general population, therefore you can only guess really. 

    I truly can not be arsed to dissect the Cochrane study for the sake of arguing the toss on this board. What I can say, is that like most data you quote, you appear to cherry pick or fail to apply proper context. Your argument on efficacy of vaccinations being the prime candidate. Absent of applied context









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  • ColsCols Frets: 3727
    Snap said:
    Big sigh @Cols. Mate, I know how testing works in and out of countries.

    I was trying to make the point that if you have a controlled population where you can test everyone you will get a true picture of testing efficiency. It's impossible in the general population, therefore you can only guess really. 

    I truly can not be arsed to dissect the Cochrane study for the sake of arguing the toss on this board. What I can say, is that like most data you quote, you appear to cherry pick or fail to apply proper context. Your argument on efficacy of vaccinations being the prime candidate. Absent of applied context









    I’m sorry to hear you can’t provide a link for the PHE study to which you’re referring, and can’t be arsed to read the Cochrane Review.  There’s not much point discussing either of them further in that case.

    One more fundamental question for you; why do you think the vast majority of developed countries require a negative PCR test for entry and won’t accept a lateral flow test as evidence of COVID-free status?  
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  • russpmrusspm Frets: 345
    Been doing the test twice a week and generally no problems
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  • SnapSnap Frets: 4900
    Cols said:
    Snap said:
    Big sigh @Cols. Mate, I know how testing works in and out of countries.

    I was trying to make the point that if you have a controlled population where you can test everyone you will get a true picture of testing efficiency. It's impossible in the general population, therefore you can only guess really. 

    I truly can not be arsed to dissect the Cochrane study for the sake of arguing the toss on this board. What I can say, is that like most data you quote, you appear to cherry pick or fail to apply proper context. Your argument on efficacy of vaccinations being the prime candidate. Absent of applied context









    I’m sorry to hear you can’t provide a link for the PHE study to which you’re referring, and can’t be arsed to read the Cochrane Review.  There’s not much point discussing either of them further in that case.

    One more fundamental question for you; why do you think the vast majority of developed countries require a negative PCR test for entry and won’t accept a lateral flow test as evidence of COVID-free status?  
    Replied in wrong thread! PHE's latest technical report, have a look.

    Lateral flows for entry to country: if it were up to me, I'd be insisting on a PCR too. It's more sensitive, so less chance of something being missed. 18% is still a big margin if you are risk managing. Makes sense.

    I can't be arsed slicing and quoting the Cochrane review because I have stuff to do, other than spend ages debating in here for what will be largely a pointless exercise. I don't think your view point is movable.  I'll still pull you up though if I think you are "chattin bear" as the kids say ;)


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  • JanekLubanskiJanekLubanski Frets: 137
    I do one a week. Question...will the test show a positive of the new Delta variant?

    I think I've had symptoms....but the test says no.


    Big ugly bloke living the dream in Selby.
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  • ColsCols Frets: 3727
    I do one a week. Question...will the test show a positive of the new Delta variant?

    I think I've had symptoms....but the test says no.


    Yes, the lateral flow test will detect the Delta variant (within its limits of sensitivity).

    If you have symptoms - new continuous cough, elevated temperature, a loss or change to your sense of smell or taste  - you should self-isolate and arrange for a PCR test.  The PCR test is more sensitive than the lateral flow test.

    If the PCR test comes back negative, you don’t need to continue to self isolate.  There are a ton of other things out there which can give you a cough or a high temperature.
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  • ToneControlToneControl Frets: 9629
    Cols said:
    I do one a week. Question...will the test show a positive of the new Delta variant?

    I think I've had symptoms....but the test says no.


    Yes, the lateral flow test will detect the Delta variant (within its limits of sensitivity).

    If you have symptoms - new continuous cough, elevated temperature, a loss or change to your sense of smell or taste  - you should self-isolate and arrange for a PCR test.  The PCR test is more sensitive than the lateral flow test.

    If the PCR test comes back negative, you don’t need to continue to self isolate.  There are a ton of other things out there which can give you a cough or a high temperature.

    Delta variant symptoms

    headache, sore throat and runny nose now the most commonly reported.
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  • ColsCols Frets: 3727
    That’s going to be a real pain in the arse in hay fever season.
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  • chris78chris78 Frets: 4718
    I love the fact that people don't see the irony of the Indian variant having similar symptoms to hayfever.
    I'll make sure I self isolate for 10 days the next time my hayfever is bad
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