Lateral Flow Tests

silvercar

Sea_Shell said:

Under what circumstances would an LFT give a void result?

Would it be a faulty test kit, or does it detect that you've not done the swab properly?

If you haven’t caught enough cells on your swab, or if you have contaminated your swab.

also you only need a couple of drops of the liquid to go into the strip, if nothing happens after a few minutes add another drop as you’ve probably only dropped in air bubbles. If you pour an excessive amount you could flood the test strip and get a void result.

I don’t use a mirror, I can feel when I’ve reached the top of my nostril. Incidentally, I follow the alternative method advised in the booklet, by swabbing both nostrils rather than throat and one nostril. Twirl the swab stick 10 times in each nostril.

Sea_Shell

JJ_Egan said:

Yes i would repeat the test before reporting .

Best of 3 ?!? 😉

GDB2222

silvercar said:

Sea_Shell said:

Under what circumstances would an LFT give a void result?

Would it be a faulty test kit, or does it detect that you've not done the swab properly?

If you haven’t caught enough cells on your swab, or if you have contaminated your swab.

also you only need a couple of drops of the liquid to go into the strip, if nothing happens after a few minutes add another drop as you’ve probably only dropped in air bubbles. If you pour an excessive amount you could flood the test strip and get a void result.

I don’t use a mirror, I can feel when I’ve reached the top of my nostril. Incidentally, I follow the alternative method advised in the booklet, by swabbing both nostrils rather than throat and one nostril. Twirl the swab stick 10 times in each nostril.

Thanks. I didn’t realise that you could do both nostrils and not the throat.

wannabe_a_saver

GDB2222 said:

Batesy1976 said:

JamoLew said:

Indeed - not without its flaws but useful nevertheless and it will attract the haters

IMO this would have been better rolled out mid Dec - but there may be good reasons why not

I suspect these will be the way to go to opening up mass attendance events

As long as the Government doesn't get the results of the test I don't care.


They're too inaccurate for mass testing if the results actually get recorded (and worse yet given to the general public.)  If everyone in the country took a lateral flow test every day they'd be 67000 false positives a day, more than we've ever recorded as, loosely speaking, "confirmed cases". We'd never get out of this mess.

In case it’s not obvious to anyone, there’s no way that anybody can get the test results unless you tell them.

If you got a positive result from one of these tests, is it worth repeating the test?

Not really.  

If you get a positive, you need to go and get a PCR test regardles of if you then get a negative immediately afterwards.  Yes the first result could be a false positive, but equally the second result could be a false negative. 

billy2shots

Just to touch on accuracy.


I carry twice weekly LFD tests with my staff as well as weekly PCR tests.


So far we have conducted approx 500 LFD tests (staff and now visitors).

We have had 1 positive result (STAFF member sent home) A confirmation PCR test was also carried out (from home by the staff member) and sent away which again showed a positive result.
The staff member developed symptoms 2 days after taking the LFD. 


I was a little sceptical at first when we started using them 3/4 months ago but they are worth their weight in gold in my experience.

JamoLew

It wouldn’t be void if you dont catch enough cells - not in a way the test will recognise 

The result may be void however 

JamoLew

A great deal of it is political and public confidence.

Something is better than nothing

If false positives are confirmed (or not) via PCR it’s the false negatives that are of “concern”

BUT even if we only pick up 50% of cases - that’s an improvement on what I reckon we get now

My suspicion as with guidance etc that actual compliance in the event of a positive test will be low (hope I’m wrong)

silvercar

According to fullfact website:

99.68% of people who did not have the virus received a negative test result. In other words, very few people who do not have the virus which causes Covid-19 will be told wrongly that they do have it, after doing a lateral flow test.

However, the tests do return considerably more false negatives. Just 76.8% of people who did have the virus received a positive result (meaning the rest received false negatives). 

This percentage can vary though depending on how much virus is in the person’s system—the test detected over 95% of individuals with “high viral loads”.

It is a numbers game, so if you test 1 million people who don’t have covid, around 3,000 will wrongly have a positive result.

As we are in low covid times the current rate of infections is only 4 in a 1000. This means that if we tested 1 million people now around 4000 would have covid. But LFTs only pick up 76.8% of cases, so they would only pick up about 3,000.

So now we have 3,000 false positives and 3,000 correct positives. Hence people saying that half of all positive test results are wrong.

But in times when we have high covid rates, out of 1 million people you would get say 30,000 positives, so the ratio of correct positives to false ones is much higher.

GDB2222

The thing is, though, that, most of the transmission is apparently by people who are asymptomatic. If we picked up just 76% of asymptomatic sufferers, and IF they self-isolated, we could reduce the R rate by roughly 76%. The cases of virus would then decrease exponentially very, very fast.

We could then either open up the economy more, or we could use the very low R to drive the infection rate to almost nothing and then reopen the economy. 

It would take around 4 weeks of everyone testing to drive the number of daily cases down from several thousand to just 2 or 3 individuals, and I think that even our test and trace people could handle that.  

There would be a lot of false positives, but these people should quickly get a PCR test, and they would only have to self-isolate for a day or two before any negative cases were told that.   

onthebench

GDB2222 said:

Initially, people were worried that the swabbing would be painful, but it really isn’t. Ticklish, yes, but not painful. 

I have done a couple of tests, and I found it difficult to self administer the swabs. It helps to use a mirror. Or get someone else to do it for you.

I hate the throat swabs. In fact just thinking about it is triggering my gag reflex now. I’ve found the only way I can do it is as quickly as possible, which then tends to make it a bit painful as I end up stabbing my tonsils.