NHS test- how accurate is it really?(35 Posts)
Posting on behalf of a close friend who has just been given supposed odds of 1/2 chance of downs in the NHS testing. This is based on age (39), slightly high nuchal and higher hcg/lower PAP A than expected. However, I'm not convinced.
Isn't it totally possible (or likely in fact?) that this has just come about due to a combination of unlucky factors, appearing to point to something, when in fact, it's all fine and the NHS test is just a bit crap?
She's now waiting for harmony results, so am keeping my fingers ridiculously crossed that my theory will pan out.
What do people think?
You're not convinced? Based on what?
The combined screening does have a false negative and false positive rate, which is why you will only ever get a risk ratio and not a definite yes/no.
rhe test combines NT measurement (raised often with trisomy 21), alongside other markers which occur in varying levels in maternal serum, based on different trisomys. A 1:2 result is a high enough chance to warrant further testing imo, despite that the screening isn't conclusive on its own.
But I'm not sure why it's anything to do with you or why you'd need to prove your theory, which is based on what evidence? Genuinely interested what has made you think that the test, which is offered to every pregnant woman, isn't good enough?
Are you a doctor?
If not it's the doctor's opinion which ought to count for your friend, not yours.
There's a 50% chance that her baby has Down's and a 50% chance that "a combination of unlucky factors, appearing to point to something, when in fact, it's all fine" as you say. The test is giving her odds, not a definitive answer. It's not a crap test, it's a screening test to guide whether other tests are recommended, eg amniocentesis or NIPT.
I hope the Harmony test gives her the result she is hoping for.
Has she been offered the Harmony equivalent as an NHS test? This is what happens in my area.
www.wolfson.qmul.ac.uk/service-1/antenatal-screening/screening-tests/the-combined-test Info on the performance of the test for you
Mungo- I'm basing this on the fact that the likes of harmony seem to be giving supposed "high risk" people a very a low risk, when the much more accurate test is performed. This suggests that the NHS test is potentially causing some unlucky people much unnecessary worry and heartache.
The reason it's "something to do with me" is because I care for my friend and I'm worried about her. Thanks for such an aggressive response. Really not called for in this very sensitive situation.
I also don't need to "prove" anything. I'm looking for genuine opinions based on experience.
It just gives a . risk percentage based on factors.
Sounds like she's had all the risk factor.tests and has been given a prediction. The only way to know for sure is genetic testing.
as other people have said nhs tests are indicative of risk. Usually it is expressed in terms of a 1 in 100 chance or whatever the number is. I went private for the harmony test as it wasn't available on my the Nhs and the first test didn't work ( not enough foetal blood in sample) but second test v reassuring. Didn't go for amnio ( only way to be certain) as Nhs test had come back 'v good for my age'! risk harmony v v low.
Apologies if I came across as aggressive. I was genuinely wondering what made you think it wasn't an appropriate test. Unfortunately the harmony is relatively new and isn't necessarily offered in all NHS trusts and is in the majority a private test.
The harmony is actually a very different kind of test, but as it's still new, there isn't enough research to warrant it being rolled out across the entire NHS and replacing the combined screening. Eventually it's likely that harmony will be the test ignore choice for the NHS but at the moment, combined is seen as gold standard despite it having issues with sensitivity and specificity.
As it stands, the combined test says your friend has a 50/50 chance of having an affected baby. Harmony is being used to determine whether this is accurate. Your friend would still be offered a diagnostic test if the harmony comes back as high risk.
Antenatal trisomy screening is a massive ethical grey area, but if a woman has had a test, yes, the chances are that they could be the one affected or the x amount not, which is why it's screening and not diagnostic. It's used as a method of identifying at risk pregnancies because the diagnostic test is invasive and carries a miscarriage risk. Combined screening may, in your eyes, be crap, but it's what was on offer, is seen as gold standard (at the moment) and is what your friend accepted.
Ultimately, your friend has been given a set of odds which has led to further testing so the test has done its job so to speak.
Thanks mungo - I appreciate that. I'm probably sensitive too as I'm really worried for her.
The combined test picks up something like 70-80% of trisomy issues but has a false positive rate of around 2-4%, which is to say 2-4% of women with perfectly healthy babies get a screen positive result (odds of more than 1 in 150). That may not sound like a lot but out of 100,000 normal pregnancies 2,000-4,000 women will get told they are high risk and be offered an unnecessary CVS, of which 20-80 women with healthy babies will suffer a miscarriage based on the 1-2% risk. The risk of a false positive increases hugely with age as well. Similarly, out of 100,000 trisomy pregnancies 20,000-30,000 women will get told they are low risk and then give birth to a baby with a trisomy.
The NHS obviously thinks these odds are fine but there are many women, including myself, who have been given a high risk score only for everything to be ok. If I have any more children I will be refusing the NHS test and going straight for NIPT.
The NHS classes a nuchal translucency of over 3.5mm as high risk but as far as I've read babies with trisomy problems tend to have even larger measurements of >5mm. Typical blood tests for Down syndrome would be PAPP-A 0.4MoM and free beta hCG 2.0MoM. In Edwards and Patau both of these measurements are well below the average of 1.0MoM.
There are soft markers present in ultrasound scans such as the higher rate of absence of nasal bones in babies with Down syndrome but the NHS doesn't appear to take these into consideration. The whole thing is pretty flawed really and I'm surprised the NHS is only introducing the NIPT for high risk pregnancies in 2018 when they could have a wholesale roll out across the board and have detection rates of over 99%.
I hope that's helpful and I hope your friend gets good news.
Harmony is much better than combined test IMO and there is loads of research from other countries that proves how accurate it is.
I've been through high odds back in October although they were lower than your friend. We were sort of pushed into the CVS route but it came back clear.
The NHS screening is just a risk factor as the above has said. Based on my own research from when we went through this the info you have given on age, higher NT, higher HCG and low PAPPa would give a higher risk of T21.
The Harmony test is still a screening test but a much more accurate one, if that comes back as likely for a chromosome issue then they may refer your friend for a CVS/amnio to get a diagnostic.
I wish her and you all the best as I've been through that awful waiting stage of the 'unknown'. Our risk for T13/18 was a little higher and I was more nervous about those results. Honestly I still do not know now what we would have done if our result for T21 was positive. I was completely on the fence and I am just relieved I didn't have to make a decision.
There are soft markers present in ultrasound scans such as the higher rate of absence of nasal bones in babies with Down syndrome but the NHS doesn't appear to take these into consideration.
I believe this is because soft markers are only present 50% of the time, and those aren't good enough odd for the NHS to use them as they're it deemed reliable enough. Which is where combined and quad screening is a grey area ethically as if the NHS deems 50% sensitive and specific not enough, how can they accept the odds of the combined-quad which really aren't that much higher. Screening usually brings more questions than answers and is such a tricky business.
OP, I hope that the results aren't too long to come back - it's sure to be an agonsing wait, and difficult because all you can do is wait and be supportive.
@Mungobungo there are lots of soft markers with different rates of presence in trisomy pregnancies. Studies such as this have shown that the more factors taken into consideration the more accurate the screening.
NIPT is still not validated as diagnostic though. So it may be more Accurate than NHS screening but it is not diagnostic.
I've posted some of the accuracies in a different thread but something like the IONA is over 99% accurate for all three common trisomy disorders, so it may not be truly diagnostic in the scientific sense but it's just semantics really!
I was given a 1 in 3 chance and my daughter does have DS.
Don't be worried for her. Do some sensible research, find places where DS parents converge online, read first hand accounts, blogs, find out the actual reality, rather than what the Dr's will tell her if she is "unlucky". That way she can access accurate information and make a truly informed decision that is right for her. X
Saggy- thanks. Yes, you make a good point. Will do.
I'm sorry Suzie but it's not 'just semantics'.
I offer IONA to my patients and I think it's a marvellous test and the company are fantastic... but it's NOT diagnostic & any fetal med consultant who doesn't use +ve NIPT results in conjunction with offering invasive testing is a charlatan.
I did say it's not diagnostic in the scientific sense, however for many women a result that has 99% accuracy is just as good.
No one has mentioned anyone using a positive NIPT result without a diagnostic test and the midwives where I am were very clear that a positive NIPT would mean a referral to a consultant for CVS.
With those odds she should have ga cvs if she would abort for downs . Be aware that it could be something else though if it isn't downs .
It was bad news from the harmony.
Thanks for all the input.
What can I do now to support? Ideas welcome.
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