When it comes to blood pressure, renal function, bone density and cholesterol, what does abnormal really mean?
Anyone, it seems, can create an epidemic. Witness a recent article in the Fairfax papers that provides “startling” news about the large number of Australians with high cholesterol who don’t even know they have it – an epidemic of high cholesterol!
Here’s an easy way to create your own epidemic that avoids handling any biological materials.
Choose any symptomless risk factor (such as a blood test or a physiological measure like blood pressure). Then propose that anyone with a single measurement above the median is at “above average risk”.
Give that risk group a medical label (“hyper-risk-factorosis”, for instance) then suggest that people with this label should be found and treated.
This process – with some nuances – has been applied to many risk factors such as blood pressure (hypertension), renal function (chronic kidney disease), bone density (osteopenia and osteoporosis) and, as above, cholesterol (hyperlipidaemia).
The same logic would suggest that since being male raises many disease risks (by as many of these risk factors), we might label all males as having “X-chromosome deficiency disorder”.
Does the label help or harm?
Of course, for people with very high levels of some risk factors, treatment may be worthwhile. Medication for people with very high blood pressure, for instance, has prevented many strokes.
But we also need to consider the downside of drawing a line across the risk factor level: the labelling of a large, and mostly asymptomatic, segment of the population as having a medical condition.
The label itself can have psychological and social impacts. But labelling a risk factor as a medical condition also stimulates the therapeutic reflex to treat. For low-risk patients, that treatment may have minimal or no benefit yet risk all the adverse effects.
If these harms are outweighed by the benefits of treatment, then the labelling and diagnosis may be justified.
But the guideline panels defining diseases have usually provided little evidence to justify changing the definitions of diseases and rarely consider the harm the changes may cause. In fact, harms are are often rapidly dismissed on the few occasions they are mentioned.
Surprisingly, there’s no internationally agreed process for defining diseases. And even more importantly, there’s no agreed process for deciding where to draw the line across the spectrum of a risk factor that divides “normal” from “abnormal”.
Are we all abnormal now?
This has made me permanently sceptical about studies that look at the prevalence of risk factors.
A recent ABS survey, for instance, suggested 33% of Australian adults had “abnormal” cholesterol but many were “undetected”.
Aside from the problems of labelling someone based on a single measurement, there are several concerns in this judgement.
First, the dividing line between normal and abnormal is arbitrary. The fact the survey concluded “one in three Australians aged 18 years and over (32.8% or 5.6 million people) had abnormal or high total cholesterol levels” suggests “abnormal” is also very close to average.
Second, labelling people with a single risk factor as “abnormal” also ignores that fact that cholesterol alone is a weak predictor of future heart attacks.
Only when we combine all the weak risk predictors – age, smoking, cholesterol, blood pressure, diabetes – is there a reasonable chance of saying who is at increased risk.
Most guidelines now only suggest treating cholesterol if there is sufficient risk based on a combination of these risk factors.
Be still, my beating heart
But don’t panic yet. Deaths from heart disease have been steadily declining for decades.
As a 2011 report from the Australian Institute for Health and Welfare concluded:
The overall death rate for CVD [cardiovascular disease] has fallen by about 80% since the 1960s and continues to fall. Death rates for the major types of CVD, such as coronary heart disease, stroke, heart failure, rheumatic heart disease and peripheral vascular disease, have all fallen markedly in the past 20 years.
We can thank much better treatment after the first heart attack for some of this decrease in mortality. But incidence of cardiovascular disease has also fallen, probably due to declines in smoking (reduced by more than 30% in the past 20 years) as well as better management of risk factors such as blood pressure and lipids.
This should be cause for some celebration, rather than a panic about undetected risk factors.
Paul Glasziou was on the management committee for two large cholesterol-lowering trials. He is on the Board of Therapeutic Guidelines and the BMJ.