Preparing for Ambulatory Blood Pressure Testing

Ambulatory blood pressure measurement (ABPM) refers to the measurement of your blood pressure over the course of 24 to 48 hours, using a portable digital blood pressure monitor. The monitor is usually fitted for you at your local clinic or hospital outpatient department and it looks like a normal blood pressure cuff that is attached to a small device which is worn on your belt for the next day.

This machine will prompt inflation of the cuff at regular intervals of 15 to 20 minutes during the daytime for serial measurements of your blood pressure, and at 30 to 60-minute intervals while you sleep. It will store your readings, which will be retrieved for analysis when you return the monitor the next day.

The average daytime, nighttime, and 24-hour blood pressures are calculated by a computer. You can also find out the number of abnormally high blood pressure measurement during the monitoring period. Other information obtained from this data is also used to help determine your cardiovascular risk and risk of progression to end-stage renal (kidney) disease, a complication of hypertension.

Doctor putting a blood pressure cuff on a woman
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Why Would Your Healthcare Provider Recommend ABPM?

Ambulatory blood pressure monitoring can determine what your blood pressure is like under normal circumstances during a day. You may particularly experience “white coat hypertension,” which refers to elevated readings only at the practitioner’s office. This can be the result of anxiety or even occur after rushing around to get to your appointment.

With ABPM, white coat hypertension is no longer an issue. Other patients have evidence of complications of high blood pressure but they have normal office measurements over time. These patients may have “masked hypertension,” which is associated with increased risk of health problems due to cardiovascular disease.

If your healthcare provider suspects you have a reason to experience episodes of hypertension periodically during the day, then ABPM is the best way to explore that possibility. Similarly, if you are already taking medication for high blood pressure but sometimes experience symptoms of low blood pressure, such as dizziness or light-headedness, then ABPM will be helpful for evaluation of your symptoms.

In some cases, your healthcare provider may simply want to be certain that your regimen is working throughout the day. Most individuals have a drop in blood pressure at night, but when that does not occur, it is associated with significant cardiovascular problems, including increased size of the left ventricle of the heart and heart failure. Nighttime hypertension is a better predictor of mortality due to cardiovascular disease compared to daytime blood pressure, and it can be identified through ABPM.

Should Everyone Undergo Ambulatory Blood Pressure Measurement?

Some experts in the United States recommend the use of ABPM to confirm a new diagnosis of high blood pressure when an elevated reading occurs in the practitioner’s office or outpatient clinic. One expert group that makes this recommendation is the United States Preventive Services Task Force, which weighs all the potential risks and benefits of preventive healthcare measures before making a recommendation.

The USPSTF has based this recommendation on the evidence that suggests the risk of fatal and nonfatal cardiovascular events and strokes is strongly associated with the high ambulatory blood pressures. Other groups have not made the same recommendation in routine cases of uncomplicated high blood pressure, primarily because ABPM is less convenient and more expensive compared to traditional office blood pressure measurements.

In some cases, healthcare providers will ask their patients to make serial blood pressure measurements at home as an alternative to ambulatory blood pressure monitoring. There are several circumstances that most experts agree should prompt ABPM, including white coat hypertension and hypertension that does not improve with increased medication.

Will the Results of ABPM Change My Treatment?

When used for the reasons mentioned above, one study found that ABPM resulted in a change in treatment for hypertension in almost half of all patients tested, resulting in improvement of blood pressure control. A change in timing of blood pressure medication doses may result in significant improvement after ABPM in individuals whose once-daily medications may not be effective for a full 24 hours.

Getting the Most Accurate Results

There are several things you should do to ensure your test is accurate and reflective of your blood pressure throughout a routine day. When the machine is preparing to take a measurement of your blood pressure, you will hear a beep. When this occurs, sit down if you can, keeping the blood pressure cuff at the same level as your heart.

Be sure the tube between the cuff and machine is not kinked or twisted and try to keep your arm still and steady while the machine is taking a measurement. Your healthcare provider will ask you to keep some type of diary or record of your activities before each blood pressure reading, so after the machine completes measurement, write your entry. You should also note your bedtime, time of awakening, and medication times.

Bottom Line

Ambulatory blood pressure monitoring provides accurate measurement of your blood pressure throughout the course of your day and night. Although most experts agree that it is the best method for evaluating specific blood pressure problems that may not be evident at your practitioner's office, standard home blood pressure measurements provide similar information and may be adequate for evaluation of your blood pressure. Your healthcare provider will tell you if ambulatory blood pressure monitoring should be a consideration, based on your individual medical evaluation and his clinical impression.

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By Karen Shackelford, MD
Karen Shackelford, MD, is an emergency medicine physician with years of experience helping patients dealing with blood pressure issues.