12 Steps to Diagnose High Blood Pressure – Understanding Hypertension

High blood pressure (BP), also called hypertension, increases the risk of heart disease, stroke, and kidney disease. It is one of the most important causes of premature death worldwide.

In 2025, an estimated 1.56 billion adults will be living with hypertension (1). According to the World Health Organization (WHO), hypertension kills nearly 8 million people every year.

Overall, approximately 20% of the world’s adults are estimated to have hypertension. In 1991, the National High Blood Pressure Education Program (NHBPEP) estimated that 43.3 million adults had hypertension in the United States (2). The prevalence dramatically increases in patients older than 60 years.

12 Steps to Understand How to Diagnose High Blood Pressure (Hypertension)
It is crucial for health professionals and patients to understand how BP is measured, how hypertension is diagnosed and what are the most common pitfalls to avoid when deciding if hypertension is present or not.

1. The Definition of Blood Pressure

Each time the heart muscle contracts it pumps blood into the arteries to supply the tissues and organs of the body with oxygen-rich blood. BP is the measure of pressure in the arteries. This may be compared to the pressure of water in a garden hose, except that the arterial wall is a living tissue.

BP is recorded as two numbers, e.g., 125/80 millimeters of mercury (mm Hg). The first number is the systolic pressure, that is when the heart muscle contracts and blood is pumped into the arteries. The lower figure, the diastolic pressure, is the pressure when the heart is relaxing and filling up with blood, between strokes.

2. The Definition of Normal Blood Pressure and Hypertension

The following is the most widely used classification of BP and hypertension (3):

  • Normal: Systolic BP lower than 120 mm Hg, diastolic BP lower than 80 mm Hg
  • Prehypertension: Systolic BP 120-139 mm Hg, diastolic BP 80-89 mm Hg
  • Stage 1 hypertension: Systolic BP 140-159 mm Hg, diastolic BP 90-99 mm Hg
  • Stage 2: Systolic BP 160 mm Hg or greater, diastolic BP 100 mm Hg or greater

In 2017, the American College of Cardiology/American Heart Association (ACC/AHA) updated their guidelines for the prevention, detection, evaluation, and management of high blood pressure in adults by eliminating the classification of prehypertension and dividing it into two levels (4).

  • Normal: Less than 120/80 mm Hg;
  • Elevated: Systolic between 120-129 and diastolic less than 80;
  • Stage 1: Systolic between 130-139 or diastolic between 80-89;
  • Stage 2: Systolic at least 140 or diastolic at least 90 mm Hg;
  • Hypertensive crisis: Systolic over 180 and/or diastolic over 120, with patients needing prompt changes in medication if there are no other indications of problems, or immediate hospitalization if there are signs of organ damage.

However, many experts have refused to give support to the 2017 ACC/AHA guidelines (5). Their main objections relate to the new hypertension classification and blood pressure target of 130 mm Hg systolic, with specific concerns about the elderly.

The American College of Physicians (ACP) and the American Academy of Family Physicians (AAFP) have issued their own guidelines for older adults (age 60 years and older) recommending a target systolic pressure less than 150 mm Hg, or less than 140 mm Hg in selected persons at high cardiovascular risk, which they conclude “provides an optimal balance of benefits and harms (6).”

3. Understanding How Blood Pressure Changes With Age

A progressive rise in BP is seen with increasing age.

However, age-related hypertension appears to be predominantly systolic rather than diastolic. The systolic BP rises into the eighth or ninth decade, whereas the diastolic BP remains constant or declines after age 40 years. Hence, pulse pressure, the difference between the systolic and diastolic blood pressure, increases with age

The prevalence of hypertension grows significantly with increasing age in all sex and race groups. It has been estimated that the incidence of hypertension increases by approximately 5% for each 10-year interval of age.

4. The Circadian Pattern of Blood Pressure

Blood pressure is typically lower at night, during sleep and then starts to rise a few hours before we wake up. It reaches a peak in the morning shortly after awakening. Then in the late afternoon and evening, BP starts dropping again.

12 Steps to Understand How to Diagnose High Blood Pressure (Hypertension)

Blood pressure is typically lower at night, during sleep and then starts to rise a few hours before we wake up. It reaches a peak in the morning shortly after awakening.

The onset of many acute cardiovascular and cerebrovascular events shows a daily pattern, with the highest incidence of morbidity and mortality in the early morning hours. Strong, although circumstantial, evidence suggests that the early morning surge in blood pressure may contribute to the onset of acute cardiovascular episodes (7).

5. Understanding How Blood Pressure Is Measured

Correct measurement of BP is essential in the diagnosis of hypertension. BP machines have to be properly calibrated, and appropriate cuff sizes have to be selected.

The patient should be in a seated position with the back supported and legs uncrossed. The diastolic pressure may be higher by 6 mm Hg if the back is unsupported and the systolic pressure may be raised by 2-8 mm Hg if the legs are crossed (8).

The patient should not talk during the procedure as it can raise the measured value by as much as 8-15 mm Hg (9)

12 Steps to Understand How to Diagnose High Blood Pressure (Hypertension)

Checking blood pressure at home (JAMA. 2017;318(3):310. doi:10.1001/jama.2017.6670)

Here is what you can do to ensure a correct reading (10):

  • Don’t drink a caffeinated beverage or smoke during the 30 minutes before the test.
  • Sit quietly for five minutes before the test begins.
  • During the measurement, sit in a chair with your feet on the floor and your arm supported so your elbow is at about heart level.
  • The inflatable part of the cuff should completely cover at least 80% of your upper arm, and the cuff should be placed on the bare skin, not over a shirt.
  • Don’t talk during the measurement.
  • Have your blood pressure measured twice, with a brief break in between. If the readings are different by 5 points or more, have it done a third time.

6. Different Measurement Strategies For Detecting Hypertension

There are three different measurement strategies to detect hypertension:

  • Ambulatory BP-monitoring (ABPM)
  • Home BP monitoring
  • Office-based measurements

Although screening for hypertension is often performed at the doctor’s office, many individuals with high BP measurements at the office will not have hypertension upon further testing (11). This is commonly due to white coat hypertension.

ABPM monitoring is the preferred method for detecting hypertension. If ABPM is not feasible, home BP monitoring may be used.

7. White Coat Hypertension

It is essential to understand that BP is not a fixed number. BP varies throughout the day in response to what we are doing and what is happening around us.

Some people with normal BP find that it spikes when they visit the doctor. This condition is called white coat hypertension or the white coat effect (also called isolated clinic or office hypertension).

The white coat effects will often happen because we are nervous about having our BP tested by a doctor or nurse.  Most of us tend to feel tenser in medical settings than we do in surroundings that are familiar to us, although we do not always notice it.

Sometimes the white coat effect may be powerful, making it impossible to establish a correct resting blood pressure in the doctor’s office. Hence, it is imperative not to rely on office-based BP measurements when diagnosing hypertension.

People with white coat hypertension may sometimes be at increased risk for cardiovascular events and can go on to develop hypertension. Hence, close follow-up is recommended (12).

The white coat effect may persist for years. It may be avoided by using ABPM or home-based BP-monitoring.

8. Ambulatory Blood Pressure Monitoring (ABPM)

ABPM is performed by using a small digital BP machine, usually attached to a belt around the body and connected to a cuff around the upper arm. The device takes BP measurements regularly over a 24-48 hour period, usually every 15-20 minutes during daytime and every 30 to 6 minutes during nighttime.

The BP measurements are recorded on the device, and the average day (diurnal) and night (nocturnal) BPs are determined from the data by a computer.

ABPM has been considered to be the reference standard for the diagnosis of hypertension and is a better predictor of cardiovascular disease risk as compared with conventional office-based measurements (13).

Ambulatory blood pressure monitoring (ABPM) is performed by using a small digital BP machine, usually attached to a belt around the body and connected to a cuff around the upper arm

9. Reference Values for Ambulatory Blood Pressure Monitoring (ABPM)

When ABPM is used, hypertension is defined as a 24-hour average BP greater to er equal to 125/75 mm Hg (13).

A 24 hour mean BP during ABPM of 115/75 is considered normal and mean BP higher than 125/75 is considered too high.

When looking at individual measurements, normal ambulatory blood pressure should not be above 135/85 mm Hg during the day and not above 120/70 mm Hg at night. Levels above 140/90 mm Hg during the day and 125/75mm Hg at night should be considered as abnormal (13).

10. Dipping and Non-Dipping

The average nighttime BP is approximately 15 percent lower than daytime values. People who undergo this normal physiological change are described as dippers.

Failure of the blood pressure to fall by at least 10 percent during sleep is called non-dipping.

The underlying mechanisms of non-dipping are unknown, but melatonin may play a role (14).

Non-dipping may be associated with increased cardiovascular risk (15).

11. Home Blood Pressure Measurements

Relatively inexpensive semiautomatic devices may be used for home BP measurements. These measurements correlate more closely with the results of 24-hour ABPM than with BP taken in the clinician’s office (16).

The optimal schedule for home blood pressure measurements is unclear. Evidence suggests that 12-14 measurements should be obtained to assess blood pressure correctly. These should include both morning and evening measurements during one week (17).

While seated, the patient should take two measurements (separated by one to two minutes) in the morning and the evening for at least three, and preferably seven consecutive days. Measurements from the first day should be discarded; the home blood pressure is defined as the average of all remaining measures.

It is important to acknowledge that home BP measurements may vary widely depending on factors such as stress caffeine intake, smoking, exercise and natural circadian variation.

12. Office-Based Blood Pressure Measurements

Despite their limitations, office-based BP measurements continue to be the primary technique used worldwide for the detection and management of hypertension.

Clinicians and patients should be aware of the possibility of white coat hypertension.

Multiple measurements on different days may be necessary. The patient should sit quietly for five minutes before the BP is measured. Patient position, cuff size, and cuff placement are all important.

The Bottom-Line

It is crucial for health professionals and patients to understand how BP is measured, how hypertension is diagnosed and what are the most common pitfalls to avoid when deciding if hypertension is present or not.

Office-based BP measurements are of limited value because of the frequency of white coat hypertension.

Ambulatory blood pressure measurements (ABPM) are considered to be the reference standard for the diagnosis of hypertension and provide a better predictor of cardiovascular disease risk as compared with conventional office-based measurements.

It is important to acknowledge that reference values for ABPM measurements are different from those used for office-based measurements.

If ABPM is not feasible, home BP monitoring may be used. Educating patients about when and how to perform such measurements is of crucial importance.

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