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Test and retest until you are positive
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A colleague with an aged patient in a care home says the staff are tested every week. No problem last couple of months but in the most recent test two asymptomatic carers were positive. They were negative on retest, but the initial positive was enough to enforce a lockdown and she's upset as she can no longer visit her parent.
I fully agree that it's better to be safe than sorry. However, the more we test the more the issue of false positives will come up with current estimates of 1-5 % for the PCR swab. To put it another way, you're as likely to become pregnant using a condom as having a false positive Covid test. Neither is common but they do occur.
Going back to care homes, NHS and other places that are repeatedly testing large numbers of people, false positives will be inevitable. In fact, it would be even odder if nobody tested positive over a period of time. The same should apply to passengers who get tested at an airport upon arrival. From a single planeload, one or more unlucky passengers are statistically likely to be false positive.
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I'm having to self isolate as a "close contact" tested positive. They had no symptoms, this was a surveillance test. The retest was negative yet all the close contacts still have to isolate. It's an absolute shambles tbh. |
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"I'd say the best course of action would be to retest an asymptomatic positive.
Chances of two false positives should be minimal."
Fully agree, but for the care home the first positive is enough to force lockdown, apparently that is the government policy. |
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By (user no longer on site)
over a year ago
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"I'd say the best course of action would be to retest an asymptomatic positive.
Chances of two false positives should be minimal.
Fully agree, but for the care home the first positive is enough to force lockdown, apparently that is the government policy."
I work in a care home and decline the weekly testing for various reasons. This just adds to the reasons not to be tested for me   |
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"You are more likely to get a false negative than false positive. Make of that what you will."
Actually I believe the quoted rates for both false positives and negatives are similar - lower than 5%. The issue is self administered tests, if the swab is not taken properly then the result may be a false negative. |
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"You are more likely to get a false negative than false positive. Make of that what you will.
Actually I believe the quoted rates for both false positives and negatives are similar - lower than 5%. The issue is self administered tests, if the swab is not taken properly then the result may be a false negative."
Totally agree especially about the sampling. |
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"You are more likely to get a false negative than false positive. Make of that what you will.
Rationale please. "
As explained above for a perfect sample the chances of get a false positve or false negative are pretty much equal at around 5%. Its down to sampling. The chances of a covid positive person not taking the correct sample are quite high especially as sample collection is a little awkward and uncomfortable, people don't go deep or long enough with the swab. The only way you can get a false positive from sampling is if saliva etc from a covid positive person is introduced in to a sample. Hope that explains it. |
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In practice, we’ve had patients who have blood tests and chest x-ray that are consistent with COVID - and they’ve only had a positive test on the third / fourth swab.
I’m *much* more concerned about false negatives, because of the public health implications, in hospital and in the community. |
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"In practice, we’ve had patients who have blood tests and chest x-ray that are consistent with COVID - and they’ve only had a positive test on the third / fourth swab.
I’m *much* more concerned about false negatives, because of the public health implications, in hospital and in the community."
Did you continue to test after the positive result? |
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The policy's are there to protect your colleagues relative,and all that work and live at the care home
I know as I work in a care home that it can be very upsetting to not see relatives,However these temporary lockdowns are better not to see a relative for a little while rather than not all,if the worse happens 
They can speak to the carehome as they do offer other ways to keep in touch,phone calls or video links
Whether they are really positive or a false positive I believe this is the best route, I would rather my residents etc stay safe and well.Me included |
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By (user no longer on site)
over a year ago
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"The policy's are there to protect your colleagues relative,and all that work and live at the care home
I know as I work in a care home that it can be very upsetting to not see relatives,However these temporary lockdowns are better not to see a relative for a little while rather than not all,if the worse happens
They can speak to the carehome as they do offer other ways to keep in touch,phone calls or video links
Whether they are really positive or a false positive I believe this is the best route, I would rather my residents etc stay safe and well.Me included"
I don't understand the logic of people being mad at care homes for being over-cautious when the alternative is to not be cautious enough and for vulnerable people to die. |
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"The policy's are there to protect your colleagues relative,and all that work and live at the care home
I know as I work in a care home that it can be very upsetting to not see relatives,However these temporary lockdowns are better not to see a relative for a little while rather than not all,if the worse happens
They can speak to the carehome as they do offer other ways to keep in touch,phone calls or video links
Whether they are really positive or a false positive I believe this is the best route, I would rather my residents etc stay safe and well.Me included
I don't understand the logic of people being mad at care homes for being over-cautious when the alternative is to not be cautious enough and for vulnerable people to die."
Me too x we get alot of grumpy relatives complaining,as policy is only one visitor (a bubble) we have to keep them safe |
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Unfortunately the testing process is 100% reliable, mainly because it is impossible to guarantee that the sample is taken from an exact spot with viral material present. It is quite easy to get false negatives. A false positive however requires a contamination, the test can-bot produce a false positive, if there is no viral RNA present then it can't be detected.
Cal |
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"Unfortunately the testing process is 100% reliable, mainly because it is impossible to guarantee that the sample is taken from an exact spot with viral material present. It is quite easy to get false negatives. A false positive however requires a contamination, the test can-bot produce a false positive, if there is no viral RNA present then it can't be detected.
Cal"
I had this conversation with one of our senior nurses,saying that false positives can't exist as you have to have it in your system,to be detected
Off course I was told I was wrong and that nobody can get it twice,however there are some cases where people had it bad once,then had an asymptomatic positive test months later
The conversation ended with me disagreeing and him thinking he is right bit like the forum's
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Unless a test is 100% accurate, false positives and negatives are inevitable. Their importance depends on the frequency of what you are looking for.
Let us assume the test is 99.9% accurate at not giving you false positives, which sounds very good. In the UK, the Covid incidence was estimated at 1 in 2,000 in August. What happens if you then test 2,000 samples? You would expect to find 1 true positive but also 2 false positives from the 0.1% error rate.
When the incidence is low, the false positives will become similar or even higher in number than the true positives. The only solution is to retest, as it's highly unlikely for the same sample to come up false positive twice. |
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By (user no longer on site)
over a year ago
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"so what happens after the 14 day self isolation then??? Virus gone, like a normal cold or flu type virus???"
I'm assuming the rationale is - no symptoms, no virus. Unfortunately we know that not to be the case. |
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By *mmabluTV/TS
over a year ago
upton wirral |
I exept the government hs cocked this up completely but people going for test with no symptoms are in the wrong they are causing the problem.
Before covid people shot off to A&E for no reason at all now they blow there nose and get tested,it should not be allowed.
Again this stupid government is to soft |
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By (user no longer on site)
over a year ago
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The way this COULD be useful is if a large number of people come up positive in a care home.
I know someone who had one of her patients come up positive but it turned out to be a false positive. There was no massive lockdown because this patient had been isolated the whole time and no-one else in the care home came up positive.
Once they were all retested it came up as negative.
So it's better to have a few errors and re-test to eliminate them, than not test at all and miss all manner of outbreaks.
There's no real 3rd option here to choose from. |
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"The way this COULD be useful is if a large number of people come up positive in a care home.
I know someone who had one of her patients come up positive but it turned out to be a false positive. There was no massive lockdown because this patient had been isolated the whole time and no-one else in the care home came up positive.
Once they were all retested it came up as negative.
So it's better to have a few errors and re-test to eliminate them, than not test at all and miss all manner of outbreaks.
There's no real 3rd option here to choose from."
I would also bet that your sample taking is rather good by now - by the time all staff are tested once a week and all residents once a month you must be pretty nifty with a swab. |
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By *i1971Man
over a year ago
Cornwall |
"I'd say the best course of action would be to retest an asymptomatic positive.
Chances of two false positives should be minimal.
Fully agree, but for the care home the first positive is enough to force lockdown, apparently that is the government policy.
I work in a care home and decline the weekly testing for various reasons. This just adds to the reasons not to be tested for me "
Glad you think that not being tested amongst all the vulnerable people is smart. Hope you feel really smug should you be an asymptomatic carrier and take it into the home. |
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