Definition and Classification of Hypertension: An Update

Abstract

Since the publication of a paper by the American Society of Hypertension, Inc. Writing Group in 2003, some refinements have occurred in the definition of hypertension. Blood pressure is now recognized as a biomarker for hypertension, and a distinction is made between the various stages of hypertension and global cardiovascular risk. This paper discusses the logic underlying the refinements in the definition of hypertension.

Hypertension is usually defined by the presence of a chronic elevation of systemic arterial pressure above a certain threshold value. However, increasing evidence indicates that the cardiovascular (CV) risk associated with elevation of blood pressure (BP) above approximately 115/75 mm Hg increases in a log-linear fashion.^1–5 In the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC 7) a category of “prehypertension” was created using BP criteria of 120/80 mm Hg to 139/89 mm Hg.⁶ This category did not emphasize that some individuals with prehypertension already had the disease, hypertension, while others did not. In 2003, a writing group,⁷ offered a written definition of hypertension that did not depend on threshold values of BP above optimal. The purpose of this present position paper is to further refine and update the definition and classification of hypertension. It should be noted that while definitions of disease are useful for detection, management, research, and education, definitions alone do not constitute recommendations for treatment.

Definition of hypertension

Hypertension is a progressive CV syndrome arising from complex and interrelated etiologies. Early markers of the syndrome are often present before BP elevation is sustained; therefore, hypertension cannot be classified solely by discrete BP thresholds. Progression is strongly associated with functional and structural cardiac and vascular abnormalities that damage the heart, kidneys, brain, vasculature, and other organs and lead to premature morbidity and death.⁷ Reduction of BP when target organ damage is demonstrable or the functional precursor of target organ damage is present and still reversible generally reduces the risk for CV events. Note that we separate elevated BP (one manifestation of the disease) from hypertension (the disease).

Stages of hypertension

Staging of a disease process such as hypertension is an assessment of the extent to which the disease has advanced at a particular time, that is, it is a “snapshot” of the pathophysiologic process. On the other hand, total CV risk assessment is an attempt to predict the future likelihood of the occurrence of a CV event such as myocardial infarction or stroke. Staging of hypertension and total CV risk assessment are related but not identical.

Individuals are either normal or hypertensive based on their CV status. The progression of hypertension—from early to advanced—may be represented as stages 1, 2, and 3 hypertension. Each stage of hypertension is characterized by the cumulative presence or absence of markers of hypertensive CV disease (CVD) and evidence of target organ damage regardless of the BP level. For example, progression includes such parameters as microalbuminuria or evidence of left ventricular hypertrophy. The occurrence of a major CV event clearly places the progression of the disease in a more advanced category.

BP as a Biomarker for Hypertension

BP serves as a biomarker for the disease hypertension. However, individuals with the same levels of BP might have different stages of hypertension (Table I). Furthermore, some individuals may exhibit elevated BP in the absence of hypertension. For purposes of calculating total CV risk, BP should be evaluated in the context of other CV risk factors and disease markers.

Table I.   Definition and Classification of Hypertension

Classification	Normal	Stage 1 Hypertension	Stage 2 Hypertension	Stage 3 Hypertension
Definition and classification of hypertension by classifying individuals by blood pressure level or cardiovascular status; however, priority is given to cardiovascular status. ^aCardiovascular disease designation is determined by the constellation of risk factors, early disease markers, and target organ disease as listed in Tables II–IV.
Descriptive category	Normal blood pressure or rare blood pressure elevations and no identifiable cardiovascular disease^a	Occasional or intermittent blood pressure elevations and early cardiovascular disease^a	Sustained blood pressure elevations or progressive cardiovascular disease^a	Marked and sustained blood pressure elevations or advanced cardiovascular disease^a
Cardiovascular risk factors (Table II)	None or few	Several risk factors present	Many risk factors present	Many risk factors present
Early disease markers (Table III)	None	Usually present	Overtly present	Overtly present with progression
Target organ disease (Table IV)	None	None	Early signs present	Overtly present with or without CVD events

Classification of Hypertension

American Society of Hypertension: Normal

Individuals with optimal levels of BP and no identifiable early markers of CVD are considered by the American Society of Hypertension (ASH) as normal. Resting average BP levels are usually <120/80 mm Hg, but occasional elevated BPs (even to levels ≥140/90 mm Hg) may occur in these individuals. Some individuals designated as having prehypertension by JNC 7 will be classified as normal in the ASH paradigm. Accurate diagnosis in some individuals may be assisted by home BP determinations or 24-hour ambulatory BP recordings (ASH position paper on ABPM⁸).

ASH Stage 1 Hypertension: Characterized by Early CVD Markers

ASH stage 1 hypertension is the earliest identifiable stage of hypertensive disease and generally arises from circulatory, vascular, or renal adaptations to environmental or genetic stimuli. This stage is often characterized by early signs of functional or structural changes in the heart or small arteries. BP levels are above 115/75 mm Hg and may be elevated, particularly with environmental stress. Patients frequently have more than 1 CV risk factor (Table II). This category is applied only to those individuals with early disease markers (Table III), who do not show any evidence of target organ damage (Table IV).

Table II.   Cardiovascular Risk Factors

Abbreviations: CVD, cardiovascular disease; HDL, high-density lipoprotein; hs-CRP, high-sensitivity C-reactive protein; LDL, low-density lipoprotein; non-HDL cholesterol, total cholesterol − HDL cholesterol. ^aComponents of the metabolic syndrome.

Increasing age

Elevated blood pressure^a

High heart rate

Overweight/obesity

Increased body mass index

Central obesity

Increased abdominal circumference

Increased abdominal adiposity (waist-to-hip ratio)^a

Dyslipidemia

Elevated LDL or non-HDL cholesterol

Low HDL cholesterol^a

Elevated triglycerides^a

Elevated blood glucose, insulin resistance, or diabetes^a

Chronic kidney disease

Smoking

Family history of premature CVD (<age 50 y in men, <age 60 y in women)

Sedentary lifestyle

Psychosocial stressors

Elevated hs-CRP

Table III.   Early Markers of Hypertensive Cardiovascular Disease

System	Physiologic Alteration
Abbreviation: GFR, glomerular filtration rate. ^aAlso a marker of microcirculatory disease.
Blood pressure	Loss of nocturnal blood pressure dipping
	Exaggerated blood pressure responses to exercise or mental stress
	Salt sensitivity
	Widened pulse pressure
Cardiac	Left ventricular hypertrophy (mild)
	Increased atrial filling pressure
	Decreased diastolic relaxation
	Increased natriuretic peptide
Vascular	Increased central arterial stiffness or pulse wave velocity
	Small artery stiffness
	Increased systemic vascular resistance
	Increased wave reflection and systolic pressure augmentation
	Increased carotid intimal-media thickness
	Coronary calcification or stenoses by computed tomographic angiography
	Endothelial dysfunction
	Capillary rarefaction
Renal	Microalbuminuria (urinary albumin excretion of 30–300 mg/d)^a
	Elevated serum creatinine
	Reduced estimated GFR (60–90 mL/min)
Retinal	Hypertensive retinal changes

Table IV.   Hypertensive Target Organ Damage and Overt Cardiovascular Disease

System	Evidence Of Target Organ Damage And Cardiovascular Disease
Abbreviations: ESRD, end-stage renal disease; GFR, glomerular filtration rate.
Cardiac	Left ventricular hypertrophy (moderate to severe)
	Systolic or diastolic cardiac dysfunction
	Symptomatic heart failure
	Myocardial infarction
	Angina pectoris
	Ischemic heart disease or prior revascularization
Vasculature	Peripheral arterial disease
	Carotid arterial disease
	Aortic aneurysm
	Wide pulse pressure (>65 mm Hg)
Renal	Albuminuria (urinary albumin excretion >300 mg/d)
	Chronic kidney disease (estimated GFR <60 mL/min) or ESRD
Cerebrovascular	Stroke
	Transient ischemic attack
	Decreased cognitive function
	Dementia
	Loss of vision

ASH stage 1 hypertension is a critical stage to investigate on two fronts: first, to bring specific and sensitive cost-effective tests that can detect early CVD markers (Table III) into the clinic setting and, second, to determine whether early vascular derangements can be attenuated or reversed before the onset of target organ damage or overt CVD.

ASH Stage 2 Hypertension: Characterized by Diffuse Disease Markers

Individuals with ASH stage 2 hypertension (JNC 7 stage 1 hypertension) frequently have sustained resting BP levels ≥140/90 mm Hg, with much higher elevations induced by physiologic or psychologic stressors. However, individuals with numerous disease markers (Table III) or limited evidence of early target organ damage such as left ventricular hypertrophy (Table IV) are included in this group regardless of BP levels.

ASH stage 2 hypertension indicates that progressive disease has developed as a consequence of persistent functional and structural changes in BP control mechanisms and in the heart and vasculature. Some of the early target organ damage characteristic of this stage of hypertension can be detected with specialized or research studies, which should be evaluated further to determine their potential utility and cost-effectiveness in clinical settings. Risk factors that are associated with ASH stage 2 hypertension, if not modified, continue to contribute to progressive target organ disease.

ASH Stage 3 Hypertension: Overt CVD

Untreated individuals with ASH stage 3 hypertension (JNC 7 stage 2 hypertension) usually have sustained resting BP levels ≥140/90 mm Hg, and marked elevations to levels >160/100 mm Hg are common. All individuals with clinical evidence of overt target organ damage (Table IV) or CVD are included in this category, as well as those who have already sustained CV events, regardless of BP levels.

ASH stage 3 hypertension is an advanced stage of the hypertensive continuum in which overt target organ damage is demonstrable and CV events may have already occurred or are imminent. Aging and the persistence of other identifiable risk factors together with a BP elevation, if present, exacerbate and accelerate the risk of morbidity and mortality. Management strategies for this phase of hypertension are well described.⁶ Reaching this stage of hypertension means that damage to target organs as well as overt vascular, cardiac, and renal disease have already occurred or are imminent. Vigorous attempts at BP lowering as well as aggressive management of other CVD risk factors must be started promptly and sustained in these individuals to prevent or delay further progression.