How accurate are your blood pressure readings? If you’re taking your own blood pressure at home, or even if you only have it taken at your doctor’s office, there are several mistakes that can be made that will give inaccurate readings. Inaccurate readings may lead to too much blood pressure medication, or too little. Either way your health is compromised, so getting an accurate blood pressure reading is very important.
Sheramy Tsai, writing for The Epoch Times, tells us a 2021 study in the American Journal of Preventive Cardiology suggest that we should be wary of trusting the quick blood pressure checks at the doctor’s office. Only one in five cardiologists—excluding preventive cardiologists, who manage heart disease risk factors before they worsen—follow the recommended guidelines for taking blood pressure despite having confidence in their technique.
A 2019 position statement from the Lancet Commission on Hypertension Group echoed these concerns, revealing that inaccurate blood pressure readings lead to mismanagement in 20 to 45 percent of cases in clinical settings. This is often caused by outdated techniques or limited training. Even a 5-point error can shift a reading into the hypertensive range, potentially affecting up to 84 million people worldwide.
The problem may be due to medical staff rushing in a busy doctor’s office. Or it may be due to poor training of medical technicians or support staff, who may receive less formal training than nurses or doctors. But it may also be due to patients using home cuffs without complete education. This may lead to overdiagnosis and unnecessary medication.
The study identified 5 causes of inaccurate blood pressure readings:
Causes of Inaccurate Blood Pressure Readings
- Wrong Arm Position
Where you place your arm during a blood pressure check can make a big difference between a normal reading and a hypertension diagnosis, according to a recent Johns Hopkins study published in JAMA Internal Medicine. Using electronic blood pressure readings, researchers tested three common arm positions—supported at heart level, resting on the lap, and hanging unsupported—and found significant discrepancies in readings. The researchers found that when the arm rests on the lap, systolic and diastolic readings (the first and second numbers, respectively, in a blood pressure reading) can be nearly 4 mm Hg higher than the recommended position of being supported at heart level. An unsupported arm at the side led to even greater increases.
- Wrong Cuff Size
One of the simplest factors in blood pressure measurement that is often overlooked is cuff size. For an accurate reading, the cuff must correctly fit the patient’s arm. A cuff that’s too small can overestimate blood pressure, while one that’s too large may underestimate it. The association recommends the inflatable part of a blood pressure cuff, called the bladder, wrap around at least 80 percent of your upper arm. Even if the cuff looks like it fits, the bladder inside might be too small or too big. Studies show incorrect sizes are often used in clinics—particularly for patients with larger or more muscular arms.
A 2023 study published in JAMA Internal Medicine highlights the issue. It found that using a regular-sized cuff on patients needing a larger one led to inflated readings—by nearly 5 mm Hg for a patient needing a large cuff and as much as 19.5 mm Hg for one who needs an extra-large cuff.
- Crossing the Legs
Crossing your legs during a blood pressure check may seem minor, but research shows that it can significantly change the reading. A study in the Journal of Hypertension found that when participants crossed one ankle over the knee, their systolic blood pressure rose by an average of 11.4 mm Hg, and diastolic pressure increased by 3.8 mm Hg, compared with readings with feet flat on the floor.
This leg position affects blood pressure because it increases cardiac output—the volume of blood the heart pumps each minute. With more blood flowing, pressure in the arteries rises. However, because peripheral resistance, or the natural resistance in blood vessels, doesn’t adjust to offset this increase, the overall blood pressure spikes. Crossing the legs at the ankles doesn’t have the same effect on readings.
- Full Bladder
It turns out that needing a bathroom break can do more than just make you uncomfortable—it can also raise your blood pressure. Researchers found that middle-aged women holding a full bladder showed an average increase of 4.2 mm Hg in systolic blood pressure and 2.8 mm Hg in diastolic pressure compared with after they’d relieved themselves. The effect was most noticeable after three hours, though the increase didn’t continue to rise with longer durations. This suggests that although a full bladder can temporarily boost blood pressure, it’s the discomfort and tension, rather than time, that has the biggest effect.
- White Coat Hypertension
For up to a third of patients, simply visiting the doctor’s office can spike blood pressure readings—a phenomenon known as white coat hypertension. This temporary increase, often caused by anxiety, can elevate systolic readings by as much as 20 mm Hg. Dr. Evan Levine, a cardiologist and health care author, manages white coat hypertension by giving patients time to relax and repeating measurements. Studies support this approach, showing that allowing time between readings can reduce anxiety-related spikes. Levine often takes a second reading after the exam, allowing patients to settle down and ensuring more accurate results.
This last cause is one I can certainly identify with, even as a doctor myself. This highlights the importance of taking your own blood pressure at home regularly where you are relaxed and can repeat the test often for more accuracy.
