Why Tests To Assess Heart Disease Risk Are Misleading

| April 18, 2013

Generally speaking, we’re given the impression that cholesterol levels are a good predictor of risk of heart disease. The reality is, they are not. One bit of evidence I use to support this statement is the fact that in one large study, almost 75 per cent of individuals admitted to hospital for problems related to heart disease had what would be regarded as ‘normal’ or even ‘low’ levels of supposedly ‘artery-clogging’ LDL-cholesterol [1].

It would seem that measuring someone’s cholesterol level is unlikely, therefore, to be an accurate predictor of future problems, like heart disease. In recent years there has been a vogue for adding other supposed risk factors, such as blood pressure, to cholesterol in an effort to better gauge the risk of heart disease. However, it’s been noted that even when blood pressure and cholesterol levels are both taken into account, the ability for these to predict heart disease risk is extremely limited. In one study, there was found to be a 10-fold difference in risk of cardiovascular disease despite having similarly ‘raised’ levels of blood pressure and cholesterol [2].

Do the predictions become any more reliable when even more risk factors are taken into account? Recently, the journal Circulation published a study in which 25 cardiovascular disease risk calculators were compared with each other [3]. Hypothetical patients were created using variations of the following parameters: total cholesterol, blood pressure, age, gender, smoking, high-density lipoprotein cholesterol, and the presence of diabetes. The data was plugged into the calculators, and the risks generated were categorised as either ‘low’, ‘medium’ or ‘high’.

In the ideal world, the calculators would be accurate and consistent, which each hypothetical patient falling into just one category (i.e. either ‘low’, ‘medium’ or ‘high’) whichever tool was used to assess heart disease risk. However, the average number of categories generated for each patient was not 1, but 2.2. That means, in effect, that patients would often end up being categorised in both ‘low’ and ‘medium’ or ‘medium’ and ‘high’ risk groups. Also, 41 per cent of hypothetical patients ended up being categorised in all three risk groups (‘low’, ‘medium’ and ‘high’).

In other words, overall, the results were highly inconsistent. This, obviously, does not inspire confidence.

In an accompanying commentary [4], the authors admit the deficiencies of current calculators (they describe their predictive value as “modest”) and attempt to give reasons for why there is such variance between tools. They also make the point that such tools are better than calculations based on “semi-arbitrary thresholds of blood pressure and lipid levels as proxies for high [cardiovascular disease] risk”.

It seems to me that our attempts to categorise risk based on conventional tests, including cholesterol levels, is very flawed and potentially misleading. It’s just one reason why I don’t know my own cholesterol levels and have no interest in having them tested.

Here’s to a healthy heart

Dr John Briffa
Editor
for The Cholesterol Truth



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Bear in mind we are not addressing anyone’s personal situation and you should rely on this for informational purposes only. Please consult with your own physician before acting on any recommendations contained herein.


References:

1. Sachdeva A, et al. Lipid levels in patients hospitalized with coronary artery disease: an analysis of 136,905 hospitalizations in Get With The Guidelines. Am Heart J. 2009;157(1):111-117.

2. Jackson R, et al. Treatment with drugs to lower blood pressure and blood cholesterol based on an individual’s absolute cardiovascular risk. Lancet. 2005;365:434-441.

3. Allan GM, et al. Agreement among Cardiovascular Disease Risk Calculators. Circulation Published online before print 10 April 2013

4. Jackson R, et al. Vascular Risk Calculators: Essential but Flawed Clinical Tools? Circulation. published online 11 April 2013

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Category: Heart Disease

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