Cervical screening - UK

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discovolante
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Cervical screening - UK

Post by discovolante » Tue Nov 17, 2020 8:31 pm

Has the method for this changed nationwide recently, and if so why? In this post I am going to answer my own question, but open the floor to wider discussion of the various methods used, and their advantages and disadvantages.

I've had the privilege of going for a cervical screening in both England and Scotland, relatively recently. I'm sure that when I had my last one done in England they found some abnormal cells but no HPV so said don't worry about it. Then I moved to Scotland and they made me 'start again' with a test and then another in 6 months (which became nearly a year because of Covid etc). When I went the first time, they said England checked for HPV and abnormal cells, and I *think* they just checked for abnormal cells in Scotland. I went again yesterday and the nurse explained it had changed 'in Scotland' and they test for HPV first, and if that comes up positive they then test for abnormal cells. The leaflet I got with my invitation letter says 'updated March 2020' and explains that 99% of cervical cancers are caused by HPV. Obviously the info in the leaflet is going to be hugely simplified.

I just looked on the NHS England website and the method is the same, and the website was updated in March 2020.

I guess it makes logical sense that if they're going to ignore abnormal cells anyway if you don't have HPV then there's no point in doing both, but I'm not sure what 'abnormal cells' means or whether that is routinely the case - is there 'ooh they've mutated a bit but whatevs' type and a 'holy sh.t get this person into hospital now' type? Is there a high false negative rate for HPV testing? Were there a lot of false positives previously? And if England did routinely test people for abnormal cells but ignore them if there was no HPV, then why?
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Re: Cervical screening - UK

Post by discovolante » Tue Nov 17, 2020 8:47 pm

For the sake of completeness I've just looked at Wales: https://phw.nhs.wales/services-and-team ... anagement/ which seems to do it the same way as Scotland and England, Northern Ireland seems to look for abnormal cells: https://www.publichealth.hscni.net/dire ... -screening
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Re: Cervical screening - UK

Post by jdc » Thu Nov 19, 2020 12:37 am

discovolante wrote:
Tue Nov 17, 2020 8:31 pm
Is there a high false negative rate for HPV testing? Were there a lot of false positives previously?
I found this Canadian study: https://www.aafp.org/afp/2008/0615/p174 ... %20percent.
Pap smear had a sensitivity of 55.4 percent and the HPV test had a sensitivity of 94.6 percent. Pap smear had a specificity of 96.8 percent compared with 94.1 percent for the HPV test. The negative predictive value of both tests was higher than 99 percent.
From Lange's med. epi.:

Sensitivity is the probability that someone with the disease will test positive; true positives / (true positives + false negatives) *100

Specificity is the probability that someone without the disease will test negative; true negatives / (true negatives + false positives) *100

Negative predictive value is the probability that a person with a negative test doesn't have the disease; true negatives / (true negatives + false negatives) *100

So I reckon the issue with pap smears was that they led to false negatives. The paper I quote from seems to suggest that HPV testing is pretty decent and looking at this NHS page https://www.nhs.uk/news/cancer/hpv-test ... al-cancer/ it seems to have had some influence over policy?
A study from Canada found that an initial test for human papilloma virus (HPV), which causes almost all cases of cervical cancer, led to the discovery of more pre-cancerous lesions than were found with conventional smear tests.

Smear tests look for changes to cells of the cervix, while HPV testing looks for the presence of the virus.

At present, the NHS screening programme for cervical cancer starts with a smear test. Women whose smear test results show possible low-grade or borderline changes to cells will have the sample tested for HPV. Those who have low-grade changes and HPV will then be referred for further tests (a colposcopy).

However, some areas of the NHS are testing a system where HPV tests are used first. If this is successful, the NHS may switch to initial HPV testing.

This study suggests this change would lead to more cases of pre-cancerous lesions being found than under the current system.

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Re: Cervical screening - UK

Post by discovolante » Thu Nov 19, 2020 11:40 am

jdc wrote:
Thu Nov 19, 2020 12:37 am
discovolante wrote:
Tue Nov 17, 2020 8:31 pm
Is there a high false negative rate for HPV testing? Were there a lot of false positives previously?
I found this Canadian study: https://www.aafp.org/afp/2008/0615/p174 ... %20percent.
Pap smear had a sensitivity of 55.4 percent and the HPV test had a sensitivity of 94.6 percent. Pap smear had a specificity of 96.8 percent compared with 94.1 percent for the HPV test. The negative predictive value of both tests was higher than 99 percent.
From Lange's med. epi.:

Sensitivity is the probability that someone with the disease will test positive; true positives / (true positives + false negatives) *100

Specificity is the probability that someone without the disease will test negative; true negatives / (true negatives + false positives) *100

Negative predictive value is the probability that a person with a negative test doesn't have the disease; true negatives / (true negatives + false negatives) *100

So I reckon the issue with pap smears was that they led to false negatives. The paper I quote from seems to suggest that HPV testing is pretty decent and looking at this NHS page https://www.nhs.uk/news/cancer/hpv-test ... al-cancer/ it seems to have had some influence over policy?
A study from Canada found that an initial test for human papilloma virus (HPV), which causes almost all cases of cervical cancer, led to the discovery of more pre-cancerous lesions than were found with conventional smear tests.

Smear tests look for changes to cells of the cervix, while HPV testing looks for the presence of the virus.

At present, the NHS screening programme for cervical cancer starts with a smear test. Women whose smear test results show possible low-grade or borderline changes to cells will have the sample tested for HPV. Those who have low-grade changes and HPV will then be referred for further tests (a colposcopy).

However, some areas of the NHS are testing a system where HPV tests are used first. If this is successful, the NHS may switch to initial HPV testing.

This study suggests this change would lead to more cases of pre-cancerous lesions being found than under the current system.
Ahh thanks jdc! Doing the hard work so I don't have to :oops: that makes a lot of sense to my untrained eye.

I have to admit that I had just assumed they had changed the terminology from 'smear test' to 'cervical screening' because it sounded better :oops: shows how much I know, just keep me the hell away from any sexual health courses...although as it's quite a recent change maybe that was part of it. Or maybe it was always called cervical screening and we just called it a smear. I dunno.
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Re: Cervical screening - UK

Post by jdc » Thu Nov 19, 2020 6:13 pm

Not sure how consistent they were, but they were using the term "cervical screening" at least 15 years ago: https://www.google.com/search?q=%22cerv ... F2005&tbm=

NHS: https://digital.nhs.uk/data-and-informa ... -2005-2006

PHE: https://www.gov.uk/government/publicati ... ganisation

Oh, and here https://www.independent.co.uk/news/uk/s ... 42410.html "In 1988, the National Co-ordinating Network for the National Health Service Cervical Screening Programme was established."

So I reckon it was (at least officially) called "cervical screening" at least from the start of the national network in '88 and everyone just called it a smear test, giving not a sh.t what the official name was.

The 1980 Black Report has a couple of references to "cervical screening" but not in the context of official nomenclature. https://www.sochealth.co.uk/national-he ... y-and-use/

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Re: Cervical screening - UK

Post by JellyandJackson » Thu Nov 19, 2020 7:44 pm

Sorry to be the person of anecdote rather than science, but when I last had a smear they said the policy had changed, they only looked for HPV initially, and only if that was positive were more tests done. I think this was a couple of years ago but it’s not something I put in my diary.
Thanks for the research, jdc.
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Re: Cervical screening - UK

Post by Lydia Gwilt » Fri Nov 20, 2020 1:53 pm

Yes it is called a Pap smear within the field - a dr Papinicoulos developed it and you do indeed smear the sample across a microscope slide, stain them and look at them under the microscope, specifically looking for koilocytes which have particularly enlarged nuclei as a result of infection by HPV. The problem with this is it takes a lot of trained personnel, and it's very tiring to do all day long, as a result there is a risk of positive samples being missed.

Since the vast vast majority of cervical cancers (if not all) are associated with HPV infection (more than 99%) it makes sense to test for the presence of viral DNA, which can be done more accurately and automated. If DNA from a high-risk HPV type is detected then you check further. It allows more people to be tested and quicker re-tests of positive people for long term infections. The majority of HPV infections are cleared within a couple of months and have no sequelae, it is only long-term persistent infections that are a big risk.

Although many people get an HPV infection at some point, not everyone does, and the HPV vaccine, specifically the Merck vaccine Gardasil-9, is now approved up to age 46, so it might be worth thinking about - it protects against 9 HPV types.

I don't work for Merck and nor do I work in any clinical role. I do work on HPV though

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Re: Cervical screening - UK

Post by nezumi » Fri Nov 20, 2020 4:03 pm

So, am I correct in thinking that if you have a smear with the HPV test, and the HPV test comes back negative, assuming you're not at risk to catch it in the interrim, one clear test and you shouldn't need another one for life?

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Re: Cervical screening - UK

Post by Lydia Gwilt » Fri Nov 20, 2020 4:19 pm

If you never ever have any kind of sexual contact again, you're probably OK, but I don't think I would want to assume that on just one negative test. And I certainly would not recommend that - IANAD

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Re: Cervical screening - UK

Post by nezumi » Fri Nov 20, 2020 4:37 pm

Lydia Gwilt wrote:
Fri Nov 20, 2020 4:19 pm
If you never ever have any kind of sexual contact again, you're probably OK, but I don't think I would want to assume that on just one negative test. And I certainly would not recommend that - IANAD
I'm married, so that's actually a possibility :lol:

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Re: Cervical screening - UK

Post by Lydia Gwilt » Sat Nov 21, 2020 11:26 am

nezumi wrote:
Fri Nov 20, 2020 4:37 pm
Lydia Gwilt wrote:
Fri Nov 20, 2020 4:19 pm
If you never ever have any kind of sexual contact again, you're probably OK, but I don't think I would want to assume that on just one negative test. And I certainly would not recommend that - IANAD
I'm married, so that's actually a possibility :lol:
Snap! :lol:

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