Elevated blood pressure, also called hypertension, is responsible for 10 million deaths in this country a year. You may know that, ideally, blood pressure is 120/80 or lower. You may also know that restricting salt intake, along with weight loss and exercise, are the first steps to achieving that goal, but that prescription medication is often required and must be taken every day to be safe and effective.
But you may not know that measuring blood pressure accurately isn’t easy. And if it’s done incorrectly, you could wind up being undertreated or overtreated. Recent research indicates that there are quite a few things to look for in getting a correct reading:
Using an arm cuff, not a wrist cuff. A wrist cuff can be inaccurate and is not the best way to evaluate blood pressure. A small study has validated the use of a wearable watch to check BP, but this is a newer technology, not yet routinely accepted, and not yet ready for prime time.
Cuffs that are validated for clinical accuracy are more likely to be accurate.In a recent study examining 2,486 upper-arm cuff devices, only 10% were validated, 13% were classified as equivalent, and there was no evidence of validation for 73%. From 925 wrist-based devices, 5.6% were validated, 5.5% were equivalent, and there was no evidence of validation for 85%. Look for a label on the box to see if the device has been validated.
Size matters. It has been known for a long time that a too-small cuff will artificially raise blood pressure in large people. In a recent study from Johns Hopkins, more than 40% of participants were overweight. When these people, who often require extra-large cuffs, had measurements taken with a “regular”-sized adult cuff, this inaccurately increased their systolic pressure readings by an average of 19.7 mmHg and their diastolic readings by an average of 4.8 mmHg.
The same study showed that the opposite was also true. Using a large cuff for smaller people can result in artificially low BP. I saw this recently in the office when I started getting suspiciously low readings in the office when I used too big a cuff on several people with smaller arms. In the study, when people had measurements taken with a “regular” cuff and needed a smaller cuff, this inaccurately decreased their systolic pressure by an average of 3.8 mmHg and their diastolic by an average of 1.5 mmHg, and resulted in hypertension that went undetected in 22% of cases.
Operator skill, training and experience also are important. If the cuff is partially inflated, too tight or placed on the wrong part of the arm, the reading may be wrong.
Automated cuffs are accurate, especially in doctors’ offices where they have been validated, but also need to be sized and placed correctly.
Position is important. Sitting up, in a comfortable backed chair, checking with the cuff around heart level, and with feet uncrossed give the most accurate results.
If the first reading is a little high, take a total of three readings five minutes apart and average these readings.
Blood pressure can be different in each arm. A difference of 10 mmHg or more can indicate vascular disease in one arm, from decreased blood flow. It must be checked one time in both arms to know, and the higher reading is the correct pressure.
White coat hypertension can lead some people to become quite anxious in the doctor’s office, which can elevate readings. If patients are started on medications because of this, side effects from too-low blood pressure are common
Although checking blood pressure, both at home and the doctor’s office, is simple to do, many factors may lead to abnormal readings. I have had people tell me they do not want their pressure checked because they are fearful of the results. Not taking it at all is much worse than the fear, though, because untreated hypertension can lead to stroke, heart attack or death.