The Doctor’s Surgery

To screen or not to screen?

I refused a colonoscopy because I’m sceptical – and squeamish theodore dalrymple

Is prevention always better than cure?

It is worse than cure if it fails to prevent, for it both raises anxiety and costs money. In the case of mass screening, it is often not easy to decide whether the light is worth the candle.

From time to time, I receive an ‘invitation’ to undergo a colonoscopy. So far, I have always turned it down; the test for occult blood in the stool is as far as I have gone. I have always told myself that my refusal of colonoscopy is based on the lack of scientific evidence that it is beneficial. But it’s really because I do not like the idea. I am squeamish about it.

It was with some selfish pleasure, then, that I read recently in the New England Journal of Medicine the results of a trial of colonoscopy from Norway, Sweden and Poland.

People of susceptible age were randomly invited, or not, to undergo a colonoscopy as a screening for cancer of the large bowel. After ten years of follow-up, the risk of death from colon cancer was only very slightly lower in those who had been invited for screening, and the overall death rate from all causes was no different.

As is so often the case with trials, the results were not absolutely decisive. Only about 40 per cent of those invited for colonoscopy agreed to it; evidently, my mentality in this regard is commonplace. If all the people invited had accepted, the results might have been more favourable to the procedure.

In addition, the colonoscopy was carried out only once, at the beginning of the ten-year follow-up period.

If it had been repeated at, say, five years, for the 30 per cent of the patients who underwent it who had supposedly pre-cancerous polyps removed (and who might be expected to be more likely than average to develop cancer of the large bowel), the results again might have been more favourable to the procedure.

Incidentally, I have known people who seem to become almost addicted to colonoscopy and have it performed frequently, under the impression that they are thereby prolonging their life greatly. Whether they actively enjoy it I have not enquired.

To prevent a single extra case of cancer by means of a colonoscopy (and removal of pre-cancerous polyps), in the real-life circumstances in which this trial was carried out, 455 patients would have to be invited to undergo it.

That is not the same as saving a life from cancer, however, since not everyone who has the cancer dies of it.

But if every invitee had accepted the invitation, it would have required only 182 patients to undergo a colonoscopy to detect a single extra case of cancer.

Outside North Korea, however, 100-per-cent acceptance is inconceivable. And rates of acceptance varied considerably between countries: 60 per cent in Norway and 33 per cent in Poland.

Another interesting finding of the investigation was the lower-thanexpected number of cases of cancer of the large bowel. It appears that the incidence is declining rather than rising.

The authors of the paper do not speculate as to why that should be, but presumably it has something to do with diet.

Even if it is true that screening by colonoscopy does not lead to a decrease in the overall death rate, it remains possible that it allows people a better death than they otherwise would have had – if, for example, to die from cancer of the bowel were worse than to die of other diseases. That, however, would have to be shown, and I am not sure how it could be shown.

I stick to my original refusal to accept the invitation.