Blood Pressure: 6 Common Errors in Measuring It

[David Baxter PhD]

Blood Pressure: 6 Common Errors in Measuring It
by John Swartzberg, M.D., BerkeleyWellness.com
August 07, 2018

We recently discussed the revised official guidelines for blood pressure, which lowered the cutoff for hypertension from 140/90 to 130/80—as well as the debate that ensued about this change. Often lost in this discussion is that those numbers are based on the assumption that blood pressure readings are done properly and are accurate, which is often not the case outside of research settings.

“In clinics, proper measurement may be the exception . . . rather than the norm,” a recent release from the American Heart Association (AHA) stated. That’s hardly news. There is a standard way to measure blood pressure, based largely on AHA guidelines, but studies have found that, because of improper technique, real-world readings done in medical offices are usually off by at least a few points.

Such errors don’t matter if your blood pressure is far above the cutoff for hypertension, or if it is normal (below 120/80). But it could affect your treatment if you’re in the gray area in between. Here are six common errors that can lead to inaccurately elevated blood pressure readings, according to the AHA:

1. Poor sitting posture: Slouching, crossing your legs, or having unsupported feet can add 6 to 10 points to your reading. You should sit in a chair with your back supported and feet flat on the floor or a footstool.
2. Unsupported arm: If your arm is hanging or you have to hold it up, your numbers may rise as much as 10 points. Your forearm should be supported by the practitioner (or a counter or chairback) at heart level.
3. Wrapping the cuff over clothing: This can add anywhere from 5 to 50 points to your reading. The cuff should be placed on a bare arm.
4. A cuff that’s too small for your arm: This can add 2 to 10 points.
5. Talking: This can also add as much as 10 points. Stay silent and still.
6. Having a full bladder: This can add 10 to 15 points to your reading (this one surprised me). Empty your bladder beforehand.

Other pointers:
Don’t exercise, consume caffeine, or smoke during the 30 minutes before testing (of course, you shouldn’t smoke, period). Ideally, you should wait five minutes in a quiet room beforehand. Two measurements should be done at least one minute apart and the results averaged; the first reading is often misleadingly elevated, as a study in JAMA Internal Medicine in June 2018 confirmed. And blood pressure should be measured in both arms, at least at the initial visit, with the second arm tested at least five minutes later.

To raise awareness among health care providers about the importance of accurate measurement, the AHA and American Medical Association are encouraging them to enroll in a national program called Target: BP. The program will help providers identify and correct measurement errors, as well as offer guidance for creating appropriate treatment plans for patients with hypertension and for partnering with patients to enable ongoing self-management, including teaching them to measure their blood pressure accurately at home.

Meanwhile, talk with your health care provider about your blood pressure results and ask any questions you have about how the measurement is being done. Discuss lifestyle changes that can help keep your blood pressure under control. If your reading is elevated, make sure you’re retested several times before any treatment decision is made. You may be advised to measure your blood pressure periodically at home.

Better yet is ambulatory testing, which calls for wearing a device that automatically measures blood pressure and stores the results every 20 to 30 minutes for 24 to 48 hours. Such “gold standard” monitoring is endorsed by the U.S. Preventive Services Task Force and many other expert groups to confirm an elevated office reading, before drug therapy is started,in order to avoid unnecessary treatment. It can also rule out “white-coat hypertension,” which causes elevations only in a medical setting.

Also see High Blood Pressure: Your Questions Answered.

 

[David Baxter PhD]

Measuring Your Blood Pressure at Home

Measuring Your Blood Pressure at Home
by Tim Gower, BerkeleyWellness.com
September 04, 2018

If you have high blood pressure, checking it regularly at home might help you better control the condition, even if your doctor takes your blood pressure at most appointments. A British study published in March 2018 by the journal Lancet confirms previous findings that out-of-office measurements can give you additional insight into the state of your cardiovascular health.

Compared with office measurements, home monitors (see inset) provide a better picture of your average blood pressure level, predict your risk of heart attacks and strokes more accurately, and provide instant feedback as to whether your treatment regimen is working. It’s also beneficial for people with chronic kidney disease and diabetes who need to closely monitor their readings to control high blood pressure (hypertension).

Problems with clinic BP readings
Fifteen to 30 percent of people whose blood pressure is elevated when tested in a doctor’s office or other healthcare setting have normal readings when they measure their own blood pressure at home. This phenomenon is known as white-coat hypertension, which is most common in older adults. Anxiety about visiting the doctor is presumed to be the cause of artificially elevated measurements. Additional home monitoring may reveal that those patients may not need antihypertensive medications, which can cause side effects, or that they can get by with lower doses. However, people with white-coat hypertension are at increased risk for sustained high blood pressure so they still need to regularly monitor their blood pressure.

Other factors can also affect the accuracy of in-office blood pressure measurements. Having a doctor or nurse check your blood pressure is routine, but you may be surprised to learn that current guidelines list 19 requirements for obtaining an accurate measurement. They include having patients sit for five minutes before a reading with their back supported and feet flat on the ground—perching on an exam table with legs dangling is unacceptable. At least two measurements should be taken during an office visit and averaged to estimate blood pressure.

Some research suggests there can be a significant disparity between blood pressure readings taken under ideal circumstances and those that aren’t. A study published in February 2017 in the Journal of the American Heart Association bears this out: Researchers obtained in-office blood pressure measurements from 275 patients with chronic kidney disease and normal blood pressure. Each patient was retested three times after sitting alone in a quiet room for five minutes. After patients sat quietly, their readings averaged 12 to 13mmHg (millimeters of mercury) lower compared to when their readings were taken with no prior quiet time.

Benefits of home data
Participants in the Lancet clinical trial included nearly 1,200 men and women (average age, 67) with high blood pressure of 140/90mmHg or greater despite antihypertensive drug therapy. Study subjects were randomly divided into three groups. One group checked their blood pressure at home using an automated electronic monitor twice in the morning and twice in the evening the first week of each month. Patients recorded their measurements on paper for the week and mailed them to their doctors.

The second group followed a similar routine but used a telemonitor system to transmit readings electronically to their doctors. One telemonitoring benefit was that it prompted patients to alert their doc*tors if their readings were above their target level. The doctors for both groups used self-measurements to decide whether to adjust patients’ antihypertensive drug dose.

A third group served as the control and received standard management of blood pressure based on in-office blood pressure readings.

After one year, participants in both self-monitoring groups had reduced their systolic blood pressure (the top number) by 3 to 4mmHg. By contrast, patients whose blood pressure was measured only during office visits still had readings slightly higher than 140mmHg. A 3- or 4-point difference in systolic blood pressure may not seem like much, but it’s enough to reduce the risk of stroke by 20 percent and coronary heart disease by 10 percent.

One likely reason for the difference is that the patients who self-monitored and regularly communicated their readings to their doctors were prescribed more medications to reduce blood pressure than patients who were checked in-office.

Another possible reason for the differences: Previous studies have found that patients who self-monitor were more likely to adhere to their treatment as a result of being involved in their own healthcare.

Most participants were white, which may limit how much results can be generalized to other populations. Age appeared to make no difference in how effectively patients could self-check blood pressure.

Do it right
If you use a home blood pressure monitor, follow these basic rules to help ensure that you obtain accurate readings:

• Don’t smoke, consume caffeine, or exercise in the 30 minutes before checking your blood pressure.
• Don’t measure your blood pressure when you have a full bladder.
• Try to measure your blood pressure shortly before taking a dose of your anti*hypertensive medications.
• Sit on a chair with a straight back (not a sofa) quietly for at least five minutes with your feet flat on the ground. Don’t cross your legs.
• Relax, breathe normally, and don’t talk.
• Place an arm cuff on your bare arm just above the elbow. Make sure the cuff is snug and won’t slip and that it’s not squeez*ing too tightly. A cuff that’s too large or too small can cause inaccurate readings.
• Support the arm wearing the cuff on a flat surface, such as a table, at roughly the height of your heart.
• Measure your blood pressure at the same time(s) each day.
• Don’t measure when you’re under stress or anxious, which can cause an artificially high reading, or if you suspect your blood pressure is elevated.

Ask your doctor what your target blood pressure level should be. American College of Cardiology (ACC) and American Heart Association (AHA) guidelines define hypertension as a systolic blood pressure (the top number) of 130mmHg or higher, and a diastolic blood pressure (the bottom number) of 80 mm Hg or higher.

Ask how often and when to check your blood pressure. The AHA recommends taking measurements every day for one week before your next doctor’s visit. Take two or three readings one minute apart. The AHA also suggests checking your blood pressure beginning two weeks after a change in treatment.

If your device digitally stores data (most do), bring it to your next office visit; otherwise, jot down your results on paper. If your blood pressure suddenly rises to 180/120 or higher, test your measurement again in five minutes. If it’s still high, contact your doctor right away; you could be undergoing a hypertensive crisis, which could lead to a stroke if not treated. If excessive levels are accompanied by symptoms such as chest pain, trouble breathing, back pain, numbness, vision changes, or difficulty speaking, call 911 immediately.

How to Buy a Home Blood Pressure Monitor
Home blood pressure monitors, which provide a better snapshot of your average blood pressure level than office measurements, are available for purchase in drugstores or online. Some insurance plans may cover the cost of these devices. Expect to pay between $20 and $60, though some are more expensive. Since the accuracy of these devices can vary, have your doctor check yours by comparing its readings with those of his or her in-office device. Then, ask your doctor to check it yearly. When you shop, here’s what to look for:

An automatic model. Automated digital blood pressure monitors are more accurate and easier to use than manual devices that require the user to squeeze a rubber bulb to inflate the cuff. All you need to do is wrap the cuff around your upper arm and press a button to inflate it. The monitor takes your blood pressure and displays the result. Digital devices also have a memory feature for tracking your readings. Some monitors can send readings to your computer or smartphone.

An arm cuff. Arm-cuff models are usually more accurate than wrist-cuff models. If you choose a wrist cuff, be sure to have it checked for accuracy at your doctor’s office. Some people who are obese may not be able to properly wrap an arm cuff around their upper arm and may have to use a wrist cuff.

A good fit. Be sure the cuff fits around your upper arm; cuffs come in different sizes. Use the cuff’s markings that indicate proper fit. A too-large or too-tight cuff will result in an inaccurate reading.

A seal of approval. Check to see whether the device has been clinically validated using protocols established by one of these organizations: the Association for the Advance*ment of Medical Instrumentation, the British Hypertension Society, or the European Hypertension Society. A validated monitor means that the model has gone through a series of tests to confirm its accuracy. A universal standard is currently under develop*ment and expected to eventually replace existing protocols.

Also see New Blood Pressure Guidelines: The Numbers Game.

 

[Daniel E.]

Some insurance plans may cover the cost of these devices. Expect to pay between $20 and $60, though some are more expensive. Since the accuracy of these devices can vary, have your doctor check yours by comparing its readings with those of his or her in-office device.

And, at least around here, you can get a like-new, brand-name home BP monitor for $10 or less at Goodwill or other thrift stores.

Some people can get a new blood pressure monitor even on a semi-annual basis from their insurance (with their OTC wellness credits), so they donate the "old" one to Goodwill.

 

[Daniel E.]

American Update: Found out the medical clinics at the V. A. (Veterans Administration) provide free blood pressure monitors to their patients (upon request). They are nice too and include a power adapter if one doesn't want to use batteries.

 

[Daniel E.]

I noticed yesterday that Omron makes blood pressure monitors for less than $50 USD that connect with Bluetooth to their Android/iOS app as well as Amazon's Alexa and the Apple Health app.

Amazon.com: Omron 10 Series Wireless Upper Arm Blood Pressure Monitor; 2-User, 200-Reading Memory, Backlit Display, TruRead Technology, Bluetooth Personal Care

 

[David Baxter PhD]

The price is $102.32 in Canada.

 

[Daniel E.]

I should buy a van full and sell them in front of senior centers in Canada