Ambulatory Blood Pressure Monitoring: The Gold Standard for Diagnosing Hypertension
Diagnosing Hypertension in Primary Care

Hypertension is the most common condition seen in adult primary care practices. To help identify this medical condition, the U.S. Preventative Services Task Force (USPSTF) issued a Grade A recommendation stating that out-of-office measurements via ambulatory blood pressure monitor or home blood pressure monitor should be obtained prior to a hypertension diagnosis.1 As a result, ambulatory blood pressure monitoring is now considered to be the reference standard for measuring blood pressure versus in-office and home measurements.

Limitations of Measuring Blood Pressure in Clinical Settings

There are several limitations when it comes to measuring blood pressure in clinical settings. Unfortunately, even with an automatic blood pressure device, poor technique is common. Errors can be introduced by:

• Using the wrong cuff size
• Placing the cuff over the patient’s clothing
• Improper patient position (e.g., feet not on the floor, arm not at heart level)
• Failure to allow five minutes of rest
• Patient conversation
• Full bladder
• Other observer biases

When using a manual blood pressure device, additional errors can be introduced. Potential errors when using a manual sphygmomanometer include:

• Letting air out of the cuff too rapidly
• Terminal digit bias (i.e., rounding to nearest 5 or 10 mmHg)

Even when performed correctly, office blood pressure measurement has limited reliability due to the small number of readings recorded.2 In addition, office blood pressure measurement has substantial variability that can come from physiologic and external factors causing measurements to fluctuate.3 For example, clinical blood pressure can be influenced by white-coat hypertension which may result in a misdiagnosis.4
As a result, the typical practice is to base a hypertension diagnosis off repeated measurements at the same visit or over different visits.3 Unfortunately, repeat measurement protocols are rarely followed.3 Therefore, two main out-of-office measurement methods have been identified to avoid basing diagnosis off limited office measurements:

1. Ambulatory blood pressure monitoring
2. Home blood pressure monitoring

What is the Ambulatory Blood Pressure Monitoring?

Ambulatory blood pressure monitoring requires the patient to wear a monitor for a 24-hour period. A trained nurse or medical assistant fits the monitor on the patient and provides basic instructions:

• Do not remove the cuff
• Avoid strenuous activity
• Try to relax your arm when the device is taking a reading

The monitor is programmed to take a blood pressure reading automatically at desired intervals (e.g., every 30 minutes throughout the 24-hour period). If a patient’s measurements are greater than or equal to the following cut points, they can be diagnosed as having elevated ambulatory blood pressure:

• Awake average
• 135/85mmHg
• Nighttime (sleep) average
• 120/70mmHg
• 24-hour average
• 130/80mmHg

Although ambulatory blood pressure monitoring is the reference standard, there are still some difficulties with this method:

• Lack of availability as there are few providers of this service and it requires clinical staff training
• Recommended to be worn during a work day over a 24-hour period
• Limits some physical activity (e.g., swimming, running)
• Can be a nuisance
• The patient may have to repeat the session due to low-quality data or an insufficient number of readings