Ambulatory Blood Pressure Monitor: How It Works

A wearable 24-hour ABPM accurately reads blood pressure in real time

Ambulatory blood pressure monitors (ABPMs) are widely used to assess blood pressure in real time. ABPMs allow healthcare providers to assess your blood pressure during your routine activities in daily life, whether working, sleeping, or doing chores.

Because "ambulatory" refers to being in motion, the technique is preferred because the ambulatory blood pressure monitor is more accurate when compared to "whitecoat" readings altered by being in a healthcare provider's office.

This article explains what is meant by ambulatory blood pressure monitoring, how the ABPM devices work, and information about models you may want for home use.

Woman checking blood pressure in living room
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What Is an Ambulatory Blood Pressure Monitor?

Ambulatory blood pressure monitoring is accomplished with a special device that consists of a blood pressure cuff worn on your arm. It's attached to a small recording device that you wear on your belt.

You wear the ABPM device for 24 hours. Throughout that period, it records your blood pressure, typically at 15-minute or 30-minute intervals, during your routine daily activities and while you are sleeping. The ABPM provides your healthcare provider with a complete record of your blood pressure, which fluctuates (changes) throughout the day and night.

A blood pressure reading taken in a healthcare provider's office records a single value while you're at rest. The ABPM information tracks your blood pressure in real time.

The ABPM does not report merely a single value for systolic and diastolic blood pressure that supposedly represents your official “blood pressure.” Instead, it reports an entire range of (often) widely variable values throughout the course of a day or longer.

What Is the Difference Between HBPM and ABPM?

The home blood pressure monitor (HPBM) works like the ABPM but is less expensive and more readily available. It has value, notably in helping people to stick to their high blood pressure treatment plan, but may require people to write down readings instead of an automatic recording. The ABPM is preferred for diagnosing high blood pressure by the United States Preventive Services Task Force (USPSTF).

How Do You Measure Ambulatory Blood Pressure?

Using the ABPM to diagnose hypertension (high blood pressure) requires a different approach to interpreting your blood pressure recordings.

After wearing the ABPM device for 24 hours, you will follow up with your healthcare provider to review the results, which will include:

  • 24-hour average blood pressure
  • Average daytime blood pressure
  • Average nighttime blood pressure
  • Calculated percentage drop in blood pressure at night

Hypertension is diagnosed when average blood pressure exceeds one or more of the following values using ABPM:

  • 24‐hour average blood pressure: 130/80 mm Hg or higher
  • Daytime (awake) average blood pressure: 135/85 mm Hg or higher
  • Nighttime (asleep) average blood pressure: 120/70 mm Hg or higher 

Normal blood pressure of 120 mmHg over 80 mmHg does not change with an ABPM, but it is based on averages.

When Is ABPM Used?

There are several situations when ABPMs can be a valuable device for discovering high blood pressure.

White Coat Hypertension

While high blood pressure readings taken in a healthcare provider's office may truly indicate hypertension is present, sometimes that is not the case. ABPM is helpful in assessing people with white-coat hypertension, which is elevated blood pressure in a healthcare office with normal out-of-office blood pressure values.

Sustained Hypertension

Sustained hypertension is diagnosed when blood pressure readings are high in both the ambulatory setting and the healthcare office setting. The ABPM confirms that high blood pressure is present all of the time, not just in the healthcare setting.

Masked Hypertension

Masked hypertension is described as high ambulatory blood pressure with normal blood pressure measurements in the healthcare provider's office. It is estimated that masked hypertension occurs in 10% to 30% of people. Without the use of an ABPM, this type of high blood pressure may not be discovered.

Nocturnal Hypertension

Nocturnal hypertension is diagnosed when nighttime systolic blood pressure readings are above 120 mmHg or diastolic blood pressure is above 70 mmHg. Normally, blood pressure decreases at night, and most people only have blood pressure measured during the day, so the ABPM is a valuable tool for discovering this type of hypertension.

Other Uses for ABPM

Some people have wide fluctuations in blood pressure and ABPM can help with a difficult diagnosis. It's also useful to investigate whether existing anti-hypertensive medications are working, or why they're not effective.

ABPM can help in the diagnosis and treatment of some forms of dysautonomia—an autonomic nervous system disorder that can lead to intermittent and unpredictable episodes of very low blood pressure.

Are ABPMs Accurate?

Ambulatory blood pressure monitors have been tested for accuracy for almost two decades. ABPM devices have been shown to be accurate enough for routine clinical use in a variety of patients.

Accuracy in making a diagnosis of hypertension depends upon obtaining repeated blood-pressure measurements. Using ABPM devices makes this more practical. Because of the limitations of repeated in-office blood pressure measurements and inaccuracies using home blood pressure measurements, the American Heart Association recommends 24-hour ambulatory blood pressure monitoring (ABPM) as a preferred method to diagnose hypertension.

ABPM Costs and Availability

In most cases, an ambulatory blood pressure machine is provided through your healthcare provider or a specialized hypertension center. They are used as part of an ABPM exam. The devices cost between $2,000 and $2,500, even for a primary care practice to acquire.

Usually, you will use one under the healthcare provider's direction. That means the provider will give it to you for short-term use at a cost of $200 to $250. Keep in mind that insurance companies may approve its use only for certain conditions. The reimbursement rates also will vary, so check with your insurance provider for details.

Although less common, ABPM rental may be available through a pharmacy or clinic near you.

ABPM Certification

Any ABPM device you use should be validated by an accredited organization, such as the Association for the Advancement of Medical Instrumentation (AAMI) or ESH International Protocol (ESH-IP). Not all primary care providers are trained in their use, so don't hesitate to ask about training before your ABPM exam with a professional.

How Do You Prepare to Use an ABPM?

You wear the ABPM device in daily life, so there's not too much preparation. Some general tips include:

  • Choose a 24-hour period when you can be in your normal routine. This may be a weekday rather than a weekend.
  • Plan to keep a journal during the 24-hour period that includes when you wake up and go to bed, when you take medications, and when you eat. If you experience any symptoms like dizziness or shortness of breath, you should record this, too.

There are a few activities you need to avoid. During this 24-hour period, you shouldn’t:

  • Lift heavy items or engage in strenuous physical activity
  • Shower or swim
  • Remove any part of the device without first asking your healthcare provider

How to Sleep With an ABPM

It may be difficult to sleep since you're not used to having a blood pressure cuff inflate on your arm during the night. Your healthcare provider will tell you whether you can adjust your equipment while you sleep and may suggest ways to get the best quality sleep.

Try to make your sleep environment as comfortable as possible, such as:

  • Play calming music
  • Cover your windows or wear an eye mask to block out extra light
  • Set your thermostat to a comfortable temperature

Summary

Ambulatory blood pressure monitoring is a way of assessing a person’s blood pressure during their routine daily activities and during sleep. This measurement is often more accurate than those taken in a healthcare office. Ask your provider if you have questions about ABPM.

Frequently Asked Questions

  • What is the best ambulatory blood pressure monitor?

    The answer will depend on your specific needs, and usually the ABPM is given to you by a healthcare provider for an ABPM exam. But if you need to rent or buy your own, and compare features, cost, and accuracy, you can research specific models on the dabl Educational Trust website.

  • What is normal blood pressure with an ABPM?

    Normal blood pressure of 120 mmHg over 80 mmHg is the same as it is when taken with a cuff, or with a home blood pressure monitoring (HBPM) machine. The difference is that the ABPM averages the pressure across a 24-hour period. It also averages active and sleeping-hour pressures separately.

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading
Richard N. Fogoros, MD

By Richard N. Fogoros, MD
Richard N. Fogoros, MD, is a retired professor of medicine and board-certified in internal medicine, clinical cardiology, and clinical electrophysiology.