In 2018, Sean Stocker, PhD, director of Basic and Translational Research at the University of Pittsburgh Hypertension Center, conducted an experiment.
He tested 30 healthcare professionals who were attending a hypertension workshop on their ability to accurately measure blood pressure. Only three people passed.
Inaccurate blood pressure readings have real-world consequences: High blood pressure is a silent disease and a major cause of congestive heart failure, stroke, and heart attack. An error of as little as 5 millimeters of mercury can lead to incorrect hypertension classification and alter how physicians manage the condition, the American Medical Association warns. That 5-point difference could easily come from something as simple as having a snack on the way to the doctor’s office, talking during your reading, or even having a full bladder.
For many people, it comes from simply being near the doctor, in a phenomenon called white-coat hypertension. In the Systolic Blood Pressure Intervention Trial, simply using an automated office blood pressure measurement with no clinician in the room lowered patients’ blood pressure readings by five to 10 points.
Tips for success
To make sure your readings are accurate, and you’re not doing too much or too little to keep your blood pressure in a healthy range, follow these American Heart Association recommendations:
Thirty minutes before a measurement
- Avoid smoking, alcohol, and caffeine. All three can add five to 10 points to your blood pressure reading. While both systolic (top) and diastolic (bottom) readings are affected, the effects are more pronounced in the former, which is a measure of the maximum pressure your heart exerts while beating. The diastolic measurementrepresents the pressure in your arteries between heartbeats.
- Skip the snack. When you eat, your body diverts blood to the digestive tract, causing a temporary three- to four-point decrease in your blood pressure.
- Drink water. Being dehydrated can temporarily decrease blood pressure by lowering blood volume.
Immediately before a measurement
- Empty your bladder. Having a full bladder during your blood pressure test can add up 10 to 15 points to both your systolic and diastolic measurements.
- Rest in a seated position for five minutes to allow your blood pressure to stabilize.
- Make sure the cuff is the correct size. A cuff that is too small can add two to 10 points to your reading, while an overly large cuff can give falsely low readings. The cuff should cover 80 percent of the area from your elbow to your shoulder, and the inflatable portion should cover about 40 percent of the distance around your upper arm.
During the measurement
- Uncross your legs. Crossing your legs at the knee can elevate systolic blood pressure by five to eight points and diastolic blood pressure by three to five points.
- Use bare skin. Don’t put the cuff over clothing—it can cause your reading to jump 10 or more points. If rolling up your sleeve makes the sleeve tight on your arm, remove your shirt or take your arm out of the sleeve.
- Lower stress. Try to decrease stress levels by taking deep breaths before and during your test. If you’re at the doctor’s office, ask for another reading at the end of your appointment, when you may be more relaxed.
- Don’t talk. Talking to your nurse or doctor during the test could raise your measurement by 10 to 15 points.
- Compare your arms at least once. A 2014 study in the American Journal of Medicine found average differences in systolic blood pressure of about five points between arms. Most often, the right arm has a higher reading than the left. If one arm is higher, use that arm for all future measurements.
- Support your arm. Your arm should be supported by a chair arm or table at the level of your heart. If your arm is unsupported, your reading could jump 10 points. If your arm is lower than your heart, the measurement could be higher.
- Sit up straight with a supported back and feet. Poor postural support can increase your reading by six to 10 points.
Monitor at home
One of the best ways to get accurate blood pressure readings is to monitor blood pressure at home. A collection of readings more accurately portrays a person’s blood pressure over time and leads to better management. In fact, researchers reported in the Journal of Hypertension that out-of-office measurements more accurately predict cardiovascular risk than measurements the nurse or doctor takes in the office.
At the minimum, you should record measurements twice per day (before breakfast and before dinner) for two weeks after any treatment change, such as a new medication, and for one week before a doctor’s appointment.
Take at least two readings one minute apart on the same monitoring device. For best results, choose a device that has built-in memory that saves your measurements so you can share them with your physician.