Over the course of your lifetime, you’re likely to get your blood pressure measured dozens—if not hundreds—of times by your doctors. After all, blood pressure is the most important indicator of a person’s risk for heart disease, stroke and other chronic diseases.
But what if a good number of those blood pressure readings are inaccurate?
Depending on the type of error that occurs during testing, you could be misdiagnosed with high blood pressure (hypertension)…or you could have hypertension that goes undetected and untreated, increasing your risk for a heart attack or stroke.
Most of these errors raise the systolic (top number) reading—the one that doctors watch most closely as you age. That’s because diastolic (bottom number) readings peak around age 50 to 55 and may decline thereafter. Systolic numbers, on the other hand, may keep going higher.
There are guidelines for getting accurate blood pressure readings, but most people don’t know them and they’re often overlooked by health-care providers. In research published in The Journal of Clinical Hypertension, my colleagues and I studied how well medical students followed the guidelines. Only one of the 159 participants followed all 11 steps looked at in our research.
Other research found that even seasoned medical providers make the same mistakes, especially those using a sphygmomanometer, a blood pressure monitor with an inflatable cuff, a manually operated bulb and an aneroid (nonmercury) gauge that the doctor uses with a stethoscope. (Mercury sphygmomanometers have traditionally been the “gold standard.”) Human errors still are being made even with meters using the oscillometric method that relies on an automated electronic pressure sensor that is interpreted by the person conducting the test.
Among oscillometric monitors, fully automated electronic devices are the most reliable. They record multiple readings as you sit undisturbed without any medical staff in the room. Yet even if your doctor’s practice has this state-of-the-art device, testing guidelines need to be followed to get the most accurate measurement.
Steps for BP accuracy
To ensure your blood pressure is being measured accurately, follow these steps from the American Heart Association (AHA) and the American Medical Association (AMA)…
- On the day of your test, avoid caffeine, exercise and smoking (there’s never a good time to smoke!) for at least 30 minutes beforehand.
- Empty your bladder. Waiting in an exam room with a full bladder can increase your blood pressure. Helpful: When you arrive at the doctor’s office, ask if a urine sample is needed. If not, heed nature’s call before going into the exam room. If a sample is necessary, request a cup so that you can empty your bladder before seeing the doctor.
- Sit in an armchair with your back supported…uncross your legs…and place both feet flat on the floor or on a low stool.
- Support your forearm on the arm of the chair. Blood pressure is lower when the measurement site is above heart level…and higher when the measurement site is below heart level.
- Rest for five minutes before the test. This is essential to get blood pressure to its baseline (the treatment target).
- Make sure the correct cuff size for your weight is used. Many practices have only the one size cuff that came with the equipment. But a small, medium, large and extra-large cuff should be available to account for differences in body weight. Though less common than getting a too high blood pressure reading, an inaccurate low reading can result if a medium or large cuff is used on a petite woman, for instance, and high blood pressure could be missed.
- Make sure the cuff is placed over a bare arm or nothing more than very thin fabric—slip your arm out of your clothes if necessary. Thick shirts and sweaters reduce the oscillations detected by the blood pressure device. The cuff should be placed on the upper arm, level with your heart.
- No chitchat. Talking can raise blood pressure by up to 15 mm Hg—likely due to activation of the brainstem centers that govern our focusing of attention.
- Don’t use or even look at your cell phone. And skip the magazines. Such activities activate the brain centers that govern blood pressure and heart rate. Important: Have your blood pressure taken in both arms if you’ve never had that done before—there can be a 10 mm Hg to 15 mm Hg difference between the right and left arms. The arm that gives the higher reading is the one to use for future readings.
Correcting mistakes
Once you know how your blood pressure should be measured, you (as the patient) should speak up if missteps are being made. It’s your health at risk.
What’s more, that blood pressure reading is going into your medical record. If the numbers are incorrect, it can result in a misdiagnosis of hyper-
tension when it is not present, for example, or overtreatment, which can result in dizziness and light-headedness.
Talk to the doctor if the guidelines weren’t followed when he/she, a nurse or medical assistant tested your blood pressure. If your doctor doesn’t listen, get a new one. That may sound harsh, but controlling blood pressure is among the most effective strategies to help people live longer and without chronic disease, so it needs to be done correctly.
Best at-home BP testing
We all benefit from keeping an eye on our blood pressure, but it’s especially important to monitor it if you’ve been diagnosed with hypertension.
There are good oscillometric devices for home use. You can buy a high-quality device online for less than $100. Manufacturers such as Omron and Welch Allyn have developed monitors that have been scientifically validated. For a list of validated blood pressure devices, go to the AMA site ValidateBP.org.
If you don’t yet know which arm has the higher reading, take your blood pressure in both arms and use the higher one for future measurements.
Keep a log, and bring it with you to doctor appointments. Once a year, bring along your home monitor and have it checked for accuracy against a mercury sphygmomanometer or comparable device. Readings from a device that is not properly calibrated may be consistently 5 mm Hg or more higher or lower. Aneroid devices can be sent back to the manufacturer for recalibration, while oscillometric devices will need to be returned or replaced.
Be sure to ask your doctor how often you should check your blood pressure at home. He may advise you to take it daily, for example, starting two weeks after you have changed blood pressure medications. What to do: Before taking any blood pressure medication, take two measurements one minute apart in the morning…and two readings, also a minute apart, in the evening, and average the two sets.
If the readings aren’t in line with your doctor’s office reading—especially if they are higher at home—it could be a sign that you need more medication or coaching to better stick with your regimen. Not taking medications as directed is the biggest problem among people with hypertension.
