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The rise and rise of "prehypertension"
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Tom Marshall, MBChB, MSc, PhD University of Birmingham
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T.P.Marshall{at}bham.ac.uk Tom Marshall
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A quick search of Medline reveals that prehypertension was rarely used before 2003. The term was largely invented by JNC VII. From 2004 forwards there are many papers that mention it. What exactly does this word mean and why is it so persistent? It means blood pressure within or slightly above the normal range. In other words it is a way of categorising what is a continuous variable (blood pressure).
Why does it persist? Prehypertension sounds like an illness. It sounds like a necessary precursor to hypertension, part of a slippery slope. In this respect it resembles terms like "premalignant". But it is
not really the same as premaliganant, because even hypertension is simply a way of categorising a continuous variable.
There is no magic threshold of blood pressure that is free from risk of vascular disease. We have known this for decades. Higher blood pressure measns higher incidence of vascular disease. Higher is a relative term. Persons whose usual blood pressure is 115/70 mm Hg are at lower risk of
vascular disease than those whose usual blood pressure is 120/75 mm Hg and so on.
We also know that blood pressure tends to rise with age. Those with higher blood pressures when young are likely to end up with higher blood pressures when old. So what are we being told here? People with higher blood pressures than average are at higher risk of vascular disease than
average - we have known this since the first Framingham study was published decades ago.
Why does this half-baked term persist? First because it sounds like an illness it is a gift to marketers of hypotensive drugs. Indeed the TROPHY study made drew the absurd conclusion that we could prevent hypertension (a condition effectively defined as eligibility for drug
treatment) by starting drug treatment.
Another reason is that in the US there is great attachment to using categorical variables to define eligiblity for hypotensive treatment whereas in much of the rest of the world (led by New Zealand) eligibility for treatment is determined by calculating predicted incidence of
cardiovascular disease as a continuous variable. Is this just failure of imagination in the USA? Ironically, New Zealand guidelines use the US Framingham equation to predict risk, whereas in the USA it is rarely used.
The answer may be more prosaic. Most primary care physicians in the USA do not have electronic medical records. Whereas in New Zealand, Australia, UK, Netherlands and Scandinavia it is almost unheard of for a
primary care physician to lack electronic medical records. And electronic medical records make Framingham risk calculations simple. So while the rest of the world moves towards an understanding of CVD risk that is based
on predicted incidence of illness, in the USA there are simply attempts to expand the categorical variable that encompasses those defined as eligible for treatment.
Conflict of Interest: None declared |
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