Kieran Walsh: Can you crunch the numbers better than a medical calculator?

Medical risk calculators should not be a step towards cookbook medicine, but help to tease out patients’ thoughts and worries and prejudices

A 70 year old man comes to see you for a routine check of his blood pressure. He is taking an ACE inhibitor and his blood pressure is under good control. He also has type 2 diabetes. But you notice that his pulse is irregularly irregular. You explain that he is likely to have atrial fibrillation and that he needs a thorough assessment. But the patient says that he feels fine and doesn’t want any fuss. You say that it is no fuss at all but that he does need to have a full assessment. He asks why and you explain that he is at increased risk of stroke. He says he is not bothered and that any treatments will have side effects anyways.

The conversation goes on in this way until you eventually convince him to have an ECG at the very least. You are sure that you have followed evidence based guidelines, but inwardly you worry. You wonder what difference tests and treatments might make to his life. You wonder exactly how high is his risk of stroke and what side effects treatments might have. You wonder what you would do if you were the patient.

Atrial fibrillation is common and conversations like this are common too. Increasingly, well informed patients will want precise answers to their questions. The advent of evidence based medicine and new technologies mean that they will be more likely to get answers. For example, if I put this man’s clinical symptoms and signs into a medical calculator, then I will get the answer that his adjusted stroke rate is 4% per year and he should consider anticoagulation for stroke prevention.

But then there is the risk of side effects. What is his quantitative risk of bleeding when on warfarin? Well, there is another risk calculator for that. It suggests that he is at moderate risk of bleeding—having a 1-2% risk of bleeding.

Ironically, his age means that he is more likely to benefit from warfarin, but also more likely to have a major complication from warfarin.

So how much further does this progress decision making? One way in which it helps is that it moves from the general to the specific. You can be more precise with the patient as to the benefits and risks of interventions. It is also a step on the road to more personalised healthcare. You can tell him that his hypertension, type 2 diabetes, and age put him at increased risk and that you are making recommendations based on his individual demographics and clinical features.

Of course, calculators have their downsides and they are not a panacea. Like any other tool they need to be used with care. They should not be a step towards cookbook medicine. You should be sure that they apply to your patient before you use them. You should be sure that they apply to patients with multimorbidity—if your patient has multimorbidity.

One final feature of medical calculators is that they can allow doctors and patients to make decisions together and to search out and make explicit what is most important to the patient. The patient might want to avoid having a stroke at all costs. Or they might dread the inconvenience of taking warfarin or might be worried about bleeding. The patient’s opinion might be subjective and might not be based on statistical evidence. But it is still their opinion. And healthcare professionals can use calculators to tease out patients’ thoughts and worries and prejudices. This takes time and effort and patience, but will likely drive better and more genuinely shared decisions.

Kieran Walsh is clinical director of BMJ Learning and BMJ Best Practice. He is responsible for the editorial quality of both products. He has worked in the past as a hospital doctor—specialising in care of the elderly medicine and neurology.

Competing interests: Kieran Walsh works for BMJ, which produces the online clinical decision support tool BMJ Best Practice.

  • James McCormack

    I’ve very much been enjoying your BMJ blog about medical education/shared decision making etc – love that you are championing this!!!

    I just read your piece on stroke and afib and noticed that you had to use 2 calculators and even then, it seems you didn’t get an important number which is the absolute benefit of treatment. Thought you might find the following website useful that does all the calculations for you in one spot – it is the best one I have seen out there.

    In addition, not sure if you have seen this CVD risk calculator that our group developed a few years ago

    This site gives you fingertip access to the results from most of the top/important CVD trials from the last 40 years – all the absolute numbers and NNTs etc.

    Keep up the good work – we need voices like yours out there!

  • dean_jenkins

    Agree. Nice blog Kieran.

    I have found risk calculators useful for talking through the priorities for particular patients in diabetes clinic. Whilst the doctor might like a person with diabetes to exercise more, reduce weight, get their BP under control, reduce post-prandial glucose excursions, reduce cholesterol, stop smoking, etc. etc. the person who actually lives with the diabetes all year long would find tackling them all at once overwhelming. Arriving at a ‘contract’ to address one or two this time and work towards the others is a useful technique I’ve found and risk calculators help to plot scenarios. Let’s see what controlling your BP with those tablets does to your future risk!

    Spelling out the exact risks of anticoagulation, stroke risk, and AF is often a useful tactic for focussing the discussion in the borderline frail older person.

    However, I wonder what you think of the vast majority of our decisions including shared decisions with patients. We have evolved to make better decisions using ‘rules of thumb’ (heuristics) rather than exact calculations. Catching a ball is that classic example. These highly efficient ‘rules of thumb’ are worthy of uncovering in clinical encounters but will take work. They may be what will keep us ahead of the robots.