So we’re all going to get screened for our health problems, by some businessmen who’ve bought a CT scanner and put an advert in the paper maybe, or perhaps by Gordon Brown: because screening saves lives, data is good, and it’s always better to do something rather than nothing.
Unfortunately, it’s a tiny bit more complicated than that.
Screening is a fascinating area, mainly because of the maths of rare events, but also because of the ethics. Screening isn’t harmless, as tests – inevitably – aren’t perfect. You might get a false alarm, causing stress and anxiety (‘the worst time in my life’ said women in one survey on breast screening). Or you might have to endure more invasive medical investigations to follow up the early warning: even something as innocuous as a biopsy can sometimes result in harmful adverse events, and if you do a lot of those, unnecessarily, in a population, then you’re hurting people, sometimes more than you’re helping. Lastly, people might get false reassurance from a false negative result, and ignore other niggles, which can in turn delay the diagnosis of genuine problems.
Then, there are the interesting ethical issues. One of the proposed screening programmes is intended to catch abdominal aortic aneurysms earlier. An AAA is a swelling of the main blood-vessel trunk in your belly: they can rupture without much warning, and when they do, people often die fast and frighteningly. But if you know the AAA is there, and do the repair operation at your leisure before it ruptures, then survival is far better. Screening and repairing have been shown to reduce mortality by around 40 per cent, looking at the whole population, which is a good thing.
But remember, you will operate on some people – as a preventive measure, because you picked up their aneurysm on screening – who would never have died from their aneurysm: it would have just ticked away quietly, not rupturing. And some of the people you operate on unnecessarily (and remember, there’s no crystal ball to identify these people) will die of complications on the operating table. They only died because of your screening programme. It saves lives overall, but Fred Bloggs – loving husband of Winona Bloggs – who would have lived, is now dead, thanks to you.
That’s Vegas, you could say. But it’s tricky, and the sums are often close. For example, mammogram screening for breast cancer every two years has been estimated to prevent two deaths per thousand women aged fifty to fifty-nine over ten years: that is good. But achieving this requires 5,000 screenings among those thousand women, resulting in 242 recalls, and sixty-four women having at least one biopsy. Five women will have cancer detected and treated. Again, this isn’t an argument against screening, we’re just walking through some example numbers.
Although, interestingly, that’s not something everybody is keen to do with screening. People in healthcare can be zealots, and enthusiasts, and we can often project our own values and preferences onto everyone else. Researchers have studied the invitation letters sent out for screening programmes, along with the websites and pamphlets, and they have repeatedly been shown to be biased in favour of participation, and lacking in information.
Where figures are given, they generally use the most dramatic and uninformative way of expressing the benefits: the ‘relative risk reduction’ is given, the same statistical form that journalists prefer – for example, ‘a 30 per cent reduction in deaths from breast cancer’ – rather than a more informative figure like the ‘number needed to screen’ – say, ‘two lives saved for every thousand women scanned’. Sometimes the leaflets even contain borderline porkies, like this one from Ontario: ‘There has been a 26 per cent increase in breast cancer cases in the last ten years,’ it said, in scary and misleading tones. This was roughly the level of over-diagnosis caused by screening over the preceding ten years during which the screening programme itself had been operating.
These problems with clear information raise interesting questions around informed consent, although seductive letters do increase uptake, and so save lives. It’s tricky: on the one hand, you end up sounding like a redneck who doesn’t trust the gub’mint, because screening programmes are often valuable. On the other hand, you want people to be allowed to make informed choices.
And the amazing thing is, in at least one large survey of five hundred people, even when presented with the harsh realities of the tests, people made what many would still think are the right decisions. Thirty-eight per cent had experienced at least one false-positive screening test; more than 40 per cent of these individuals described the experience as ‘very scary’, or ‘the scariest time of my life’. But looking back, 98 per cent were glad they were screened. Most wanted to know about cancer, regardless of the implications. Two thirds said they would be tested for cancer even if nothing could be done. Chin up.