Hypertension is a common disorder that affects a large proportion of the community. It is usually asymptomatic and is detected on routine examination or after the occurrence of a complication such as a heart attack or stroke.  It is often referred to as the silent killer.
The definition of hypertension is based on recommendations by the American Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure,  the British Society of Hypertension,  and the European Society of Hypertension.  There are slight differences in the definition of hypertension between guidelines.
The American guidelines (JNC-7) state that a blood pressure below 120/80 mmHg is normal, 120 to 139/80 to 89 mmHg is pre-hypertension, and anything above this is abnormal. Isolated systolic hypertension is defined as an elevated systolic blood pressure of >140 mmHg with a normal (<80 mmHg) diastolic pressure. It should be noted that the more recent Joint National Commission (JNC-8) guidelines recommended revised treatment thresholds but did not redefine diagnostic categories. 
The European and British guidelines have classified a blood pressure of <120/80 mmHg as optimal. 120 to 129/80 to 84 mmHg is normal, 130 to 139/85 to 89 mmHg is high normal, and anything above that is classified as hypertension and is divided into 3 stages:
Stage 1: systolic 140 to 159 and/or diastolic 90 to 99 mmHg
Stage 2: systolic 160 to 179 and/or diastolic 100 to 109 mmHg
Stage 3: systolic 180 mmHg or higher and/or diastolic 110 mmHg or higher.
Isolated systolic hypertension is also graded according to systolic blood pressure values in the ranges indicated, provided that diastolic values are <90 mmHg.
Although different studies have used a variety of cut-off points for the diagnosis of hypertension in the community, any blood pressure over 120 mmHg systolic is associated with an increased cardiovascular risk. The importance of hypertension is its relation to other cardiovascular risk factors and consequent overall cardiovascular risk.
In the US, data from the National Health and Nutrition Survey (NHANES) suggest that hypertension has a mean prevalence of 29% in the population >18 years of age, using a cut-off value of 140/90 mmHg. This ranges from around 7% in those aged 18 to 39 years to 66% in those aged >60 years.  The prevalence seems to be higher in Western Europe.  However, as elevated blood pressure is usually asymptomatic, the exact prevalence of hypertension is difficult to assess, and is expected to rise as the 'cut-off' value for hypertension is re-defined at a lower level.
Studies have shown that treatment of hypertension can reduce the incidence of future cardiovascular and cerebrovascular events.  The aim of early diagnosis and treatment of hypertension is to lower overall cardiovascular risk and prevent cerebrovascular events. The effects of chronic hypertension on organ systems are referred to as target organ damage.
Left ventricular hypertrophy, cardiovascular disease, cerebrovascular disease, hypertensive retinopathy, and nephropathy are the most common manifestations.  The presence of left ventricular hypertrophy is a poor prognostic sign, and regression of left ventricular hypertrophy improves prognosis. 
Guidelines on the management of hypertension emphasise the importance of calculating and managing the overall cardiovascular risk of a patient, rather than focusing only on blood pressure readings. For individuals aged 40 to 70 years, each increment of 20 mmHg in systolic blood pressure or 10 mmHg in diastolic blood pressure across the entire blood pressure range from 115/75 to 185/115 mmHg doubles the risk of cardiovascular disease.  Treating associated cardiovascular risk factors such as obesity, diabetes, hypercholesterolaemia, and smoking are as important as managing hypertension in lowering overall cardiovascular risk.
Good Hope Hospital
Honorary Senior Lecturer
University of Birmingham
SN is an author of a number of references cited in this monograph.
Professor of Cardiovascular Medicine
University of Birmingham
Visiting Professor of Haemostasis, Thrombosis and Vascular Sciences
University of Aston
GL is a consultant for Bayer/Janssen, BMS/Pfizer, Biotronik, Medtronic, Boehringer Ingelheim, Microlife, and Daiichi-Sankyo; he is also a speaker for Bayer, BMS/Pfizer, Medtronic, Boehringer Ingelheim, Microlife, Roche, and Daiichi-Sankyo. GL is an author of references cited in this topic.
Professor of Epidemiology
Head of the Section of Epidemiology & Biostatistics
School of Population Health
University of Auckland
RJ declares that he has no competing interests.
Professor of Medicine
David Geffen School of Medicine at UCLA
AW declares that he has no competing interests. Unfortunately we have since been made aware that Professor Wilkinson is deceased.
Department of Clinical Pharmacology
St Mary’s Hospital
MS declares that he has no competing interests.
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