Stopping the clot

Infections, mistakes … we know that hospitals aren’t always safe. Among the dangers is the risk of blood clots, which increases the more ill and less mobile you are. Blood clots are benign enough when they remain in the calf, producing a swollen leg, but if they break away and migrate through the veins to the lung, you have a problem – pulmonary embolus, which can be fatal. Estimates suggest that around 10 per cent of hospital deaths are due to thrombosis.

So most hospitals, when admitting patients, will score them for thrombosis risk. Women who have just given birth and people with pelvic masses – tumours, for example – are at especially high risk. How do you prevent blood clots forming? By administering the opposite, blood thinners, mainly heparin, usually in the form of an injection.

At least, that’s the plan. The National Institute for Clinical Excellence (Nice) – the supposed source of cold evidence and statistics – claimed that its new guidelines on preventing clots would “help save thousands of lives”. Here we have a problem. Blood clots are not good, but neither is blood which is too thin, fails to clot properly and bleeds uncontrollably. This can cause a stroke via a bleed into the brain, or a subdural bleed, where a minor fall causes bleeding between the outer linings of the brain. Both outcomes are potentially fatal.

This is why we need evidence to help us make decisions about the risk of clots versus the side-effect of bleeding. Little is forthcoming in the Nice guidance – but it does recommend blood thinners for a very wide patient group, much wider than previously. Given this, you’d think that there would be some firm evidence of a reduction in deaths when thinners are used. There isn’t. “We generally lack evidence for reduction in all-cause mortality [death for any reason] which would require very large trials,” Nice admits.

There is no point reducing deaths from blood clots if you increase deaths by bleeding. First we need strong evidence to show whether we are more likely to die from a blood clot or from treatment to prevent one.

The General Medical Council’s Duties of a Doctor makes explicit the requirement for doctors to reduce uncertainties about the effects of treatments. I would have hoped Nice would have called for urgent trials. It would not be difficult to find enough patients to take part, for so many people are to be offered treatment.

Margaret McCartney is a GP in Glasgow

margaret.mccartney@ft.com

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