Everyone’s been there. Which one’s right?
The answer: Perhaps neither. Individual measures of blood pressure are not as accurate as taking multiple readings over a day and averaging them.
Blood pressure varies throughout the day – by about 30 points for systolic pressure, or the pressure when the heart beats – and one or two measurements in a doctor’s office may not accurately reflect the average figure, said Beverly B. Green, MD, a senior investigator at Kaiser Permanente Washington Health Research Institute in Seattle.
Average blood pressure reading is the only measurement on which a doctor can accurately diagnose and treat high blood pressure, she said. A new study by Dr. Green and other researchers at Kaiser Permanente showed that giving patients the chance to monitor their blood pressure at home could help get more reliable measurements.
Nearly one in four adults in the United States with high blood pressure are unaware they have the condition and are not getting treatment to control it. Without treatment, the condition can cause heart attacks, strokes, kidney damage, and other potentially life-threatening health problems.
Current guidelines for diagnosing high blood pressure recommend that patients whose pressure is high in the clinic get tested again to confirm the results. While the guidelines recommend home monitoring before diagnosing high blood pressure, research shows that doctors continue to measure blood pressure in their clinics for the second reading.
In their study, Dr. Green and colleagues found that home readings were more accurate than measurements taken in clinics or at pharmacy kiosks.
“Home blood pressure monitoring was a better option, because it was more accurate” than clinic blood pressure readings, Green said. A companion study found that patients preferred taking their blood pressure at home.
For their study, Dr. Green’s group used Kaiser’s electronic health record system to identify people at high risk for high blood pressure based on a recent clinic visit. They then randomly assigned the participants to get their follow-up blood pressure readings in the clinic, at home, or at kiosks in clinics or pharmacies.
Each participant also received a 24-hour ambulatory blood pressure monitor (ABPM). These devices, which people must wear continuously for 24 hours, have cuffs that inflate every 20-0 minutes during the day and every 30-60 minutes at night. Although ABPMs are the preferred test for accurately diagnosing high blood pressure, they aren’t available for widespread use.
The Kaiser researchers found that people’s systolic BP readings at clinics were generally lower than their ABPM measurements, leading to undiagnosed high BP in more than 50% of cases. Kiosk readings were much higher than the ABPM measurements and tended to overdiagnose high BP.
The value of home monitoring
Branden Villavaso, a 48-year-old attorney in New Orleans who was diagnosed with high BP at age 32, attributes his condition to genetics. He says an at-home monitor plus the occasional use of an ABPM finally provided his doctor with an accurate assessment of his condition.
Thanks to this aggressive approach, over the past 3 years, Mr. Villavaso’s diastolic reading has dropped from a previous range of between 90 and 100 to a healthier but not quite ideal value of about 80. Meanwhile, his systolic pressure has dropped to about 120, well below the goal of 130.
Mr. Villavaso said his doctor has relied on the averages of the BP readings to tailor his medication, and he also credited his wife, Chloe, a clinical nurse specialist, for monitoring his progress.
While previous studies have found similar benefits for measuring BP at home, Dr. Green said the latest study may offer the most powerful evidence to date because of the large number of people who took part, the involvement of primary care clinics, and the use of real-world health care professionals to take measurements instead of people who usually do health research. She said this study is the first to compare kiosk and ABPM results.
“The study indicates that assisting patients with getting access to valid blood pressure readings so they can measure their blood pressure at home will give a better picture of the true burden of [high BP],” said Keith C. Ferdinand, MD, a cardiologist at Tulane University, New Orleans.
He recommended patients select a home monitoring device from www.validatebp.org, a noncommercial website that lists home BP systems that have proven to be accurate.
“We know that [high blood pressure] is the most common and powerful cause of heart disease and death,” Dr. Ferdinand said. “Patients are pleased to participate in shared decision-making and actively assist in the control of a potentially deadly disease.”
A version of this article first appeared on WebMD.com.