Last week I introduced the topic of Evidence Based Medicine (EBM). EBM is used to guide treatment in family medicine by taking into account the best available evidence, patient values and the doctor’s clinical expertise. Let’s look at cardiovascular disease (heart attack, angina, stroke, peripheral vascular disease) and how EBM plays out in deciding on a treatment plan. If you are a 60 year old woman with a family history of heart disease, a total cholesterol of 6 and a systolic blood pressure of 140, your ten-year risk of getting heart disease is 18%.
In other words there is a 1 in 5 chance that you will get some type of heart disease in that time period. Cardiovascular risk goes up with age, blood pressure, cholesterol, diabetes, smoking, family history and low HDL cholesterol. Going on a blood pressure medicine would lower the risk (for our hypothetical female patient) of cardiovascular disease by 1% and lower the risk of dying by 1% over the next 4 to 8 years (from 18% to 17%).
If this same patient went on a statin drug to lower cholesterol the drug would also lower her risk of heart disease by 1% and reduce her risk of dying by 0.5% (2% if she took BOTH the blood pressure and statin). A 1% absolute reduction in risk means 100 people would need to be treated with either a blood pressure or cholesterol drug to prevent one person from getting heart disease. Our hypothetical patient would need to consider the magnitude of benefit from the drug, the cost of the medicine and whether or not they are willing to take a pill daily to get a 1% reduction in risk for heart disease.
To one patient a 1% reduction wouldn’t be worth taking the medicine where for another, it would make perfect sense to take a medicine to get the benefit. As a patient, knowing the benefit of a treatment allows you to make an informed choice, based on your values, as to whether or not to use a medical intervention. Providers, pharmacists and online sites like the Cochrane Collaboration (canada.cochrane.org) can help you understand the absolute benefit a treatment will provide.