To screen or not to screen

There is a common assumption that screening for anything is always a good thing. But should we always be screened, or should we perhaps consider the implications before we go ahead ?

mriscanHigh-powered executives are encouraged to come for the “ultimate check-up” – MRI scans, ultrasound scans and multiple blood tests including serum rhubarb levels. We women in Luxembourg are given a pap smear, ultrasound and breast examination each time we attend the gynecologist, and encouraged to have very regular mammograms from our 40s onwards. It can be worthwhile to think a little more deeply about this question, so that we can make an informed decision about what screening we participate in.

Scans and pregnancy

When I was pregnant with my first child, the 20 week screening scan showed an abnormality in the umbilical cord. The ultra-sonographer gave me a bit of information, and told me that I needed to return for a very detailed scan with the specialist. I pushed her for more information and was told that this abnormality could be associated with chromosomal problems such as trisomy 18, or Edward’s syndrome. She didn’t know that I was a doctor, but even if I wasn’t, I could have googled it when I got home.

However, all I could remember from medical school about Edward’s syndrome was this terrifying phrase that started whizzing around my head: “Incompatible with life”. I was distraught by the time we got home, and the few days spent waiting for the detailed scan were anxious ones. My nearly nine year old is thriving, and he was a healthy baby despite his single umbilical artery.

I felt so traumatized by the whole experience that it made me question all the scans and tests that we offer in pregnancy. From being a fit and healthy young woman with a completely normal first pregnancy, I had become a patient with a potentially seriously ill baby. Even after the detailed scan, I never felt quite as confident for the rest of that pregnancy.

Now I know that most people would argue that surely it is best to know in advance if there is a problem, and in many situations this is certainly true. Babies with severe congenital heart disease can be delivered in specialist hospitals so that they can be operated on immediately after birth, sometimes surgery can even be performed in utero.  However, would I prefer to know in advance if my baby had a cleft lip, or would I prefer to carry on with a happy carefree pregnancy and discover it at birth? A really difficult one to know if you have never been in that situation.

No screening test is perfect

What we forget about screening tests is that they do not guarantee you a positive outcome – there is no perfect screening test. If there were, it would be 100% sensitive, meaning it picks up 100% of cases of the condition it is looking for. It would be 100% specific, meaning it is only positive for cases of that condition and there are no “false positives” (when a test says that you are
affected when actually you are not). Also, it would detect a condition that is very well understood and can be treated, and the treatment must then make a difference.

There has been huge debate in the medical and mainstream press over the last few years about screening for prostate cancer and breast cancer. The UK and the USA have differed dramatically in their approach to prostate cancer screening in the past.

In the US, men were positively encouraged to have the test on a regular basis. In the UK, all family doctors were issued with leaflets and advice to hand out to any patients requesting PSA (prostate specific antigen) testing. These leaflets explained that PSA testing could detect some cases of prostate cancer before they caused symptoms, but there would also be cases that were missed. Many men would also need further investigation with prostate biopsies because they had a raised PSA, but would turn out not to have cancer (false positives). For some of those with confirmed cancer, it would never have caused any problems during their lifetime, but they would still be treated and risk potential side effects from treatment such as impotence and urinary incontinence.

The current statement of the US Preventive Services Taskforce says that “current evidence is insufficient to assess the balance of benefits and harms of prostate cancer screening in men younger than age 75 years.“ For men older than 75 they conclude that the evidence suggests that screening offers more harms than benefits.

For mammography, the situation is equally confusing.  One week there will be front-page headlines about the number of lives saved by breast cancer screening, the next week we are being told about the dangers of “overdiagnosis” and the numbers of women who have been treated for breast cancers that would never have caused them any harm.

Power to the patients

I do not wish to come across as someone who is anti-screening. I have always attended regularly for my cervical smear tests and I will go for regular mammograms, but I will go for these with full knowledge of the fact that they are not perfect tests, having made an informed decision about whether I want them or not.

Which brings me on to patient information. The website does mention the downsides of mammography, and there is a leaflet sent out with your official invitation at age 50. This leaflet is rather evangelical about mammography in general, but does at least mention that occasionally breast cancers can be missed. I would like to see a leaflet available in all doctors’ rooms, especially the gynecologists, which is handed to women whenever they are referred for a screening mammogram, informing them fully and making it clear that they have a choice about whether to proceed.

The days of doctors as “Gods” who need to be obeyed without question are gone. We should be empowering our patients to take control of their own health and make their own informed decisions.


By Susie Tunstall-Pedoe, January 2013

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