Blood pressure readings differ considerably according to where and how they are taken, especially when a patient already has hypertension, according to a recent systematic review and network meta-analysis in Annals of Internal Medicine.
For an accurate diagnosis of hypertension, new standards are needed for better agreement between office, at-home, or ambulatory measurements, researchers said.
“Office blood pressure measurements may be misleading owing to white-coat or masked hypertension phenomena, and current guidelines advocate for out-of-office monitoring,” said Hao-Min Cheng, MD, PhD, a cardiologist and director of the Centre for Evidence-Based Medicine at Taipei Veterans General Hospital in Taipei, Taiwan, and an author of the study. “Only limited research has directly compared all major methods or investigated whether discrepancies fluctuate at varying blood pressure levels — an essential gap we aimed to address.”
Cheng and his colleagues observed clinically important differences between research reference office-based blood pressure measurement (OBPM) and those taken in other settings, differing from guidelines on hypertension diagnosis.
The findings also showed that differences are not fixed but depend on underlying systolic blood pressure and diastolic blood pressure levels, with divergence between office and other methods increasing when patients have higher blood pressure levels.
Cheng said he was surprised by the magnitude of the disparities and advised clinicians to account for differences when analyzing readings.
“Uniform conversions are ineffective,” he said. “Acknowledge that out-of-office measurements are typically diminished, especially during nocturnal hours, and employ BP [blood pressure]-level-specific reference values instead of standardized modifications.”
The results highlighted the need for more nuanced clinical guidance in translating blood pressure values between various settings while supporting the growing use of out-of-office measurement in diagnosis and management.
Variations in Accuracy
To compare blood pressure estimates across settings using an office reading based on a research protocol as the reference value, the investigators analyzed 65 studies involving 40,022 adults through October 2024.
Studies were included if they contained data on readings with at least two of the following methods: research OBPM taken by professionals using standardized protocols, an automated and unattended OBPM, convenient OBPM taken with no defined protocols, blood pressure measurement automatically measured at home, and ambulatory blood pressure measurement taken at regular intervals for several hours.
The biggest mean difference was with nocturnal ambulatory blood pressure measurement, at 18.14 mm Hg lower than the office reference. Readings taken at ambulatory settings over 24 hours averaged 8.63 mm Hg lower (95% CI, 6.97-10.28), and home readings were 4.59 mm Hg lower (95% CI, 2.83-6.34). Daytime readings taken in the ambulatory setting and automated readings in the office were 4.22 mm Hg and 4.57 mm Hg lower, respectively.
The study also showed a difference between 24-hour ambulatory and office measurement as high as 31 mm Hg for systolic blood pressures in the 180s and as low as 0 mm Hg for those in the 120s. With greater divergence from the mean reference linked to higher blood pressure levels, the variations were not likely to be random, Cheng said.
“It is often assumed that the 24-hour ambulatory BPM [blood pressure measurement] average (including both daytime and nighttime readings) for systolic BP is approximately 10 mm Hg lower than routine office measurements,” wrote Gregory Murphy, MB BCh, a cardiology fellow, and John W. McEvoy, MB BCh, PhD, a professor of preventive cardiology at the University of Galway School of Medicine and the National Institute for Prevention and Cardiovascular Health in Galway, Ireland, in an accompanying editorial.
The authors wrote that the findings support recommendations from the European Society of Cardiology in 2024 to use a systolic blood pressure treatment target of 120-129 mm Hg no matter if measured in the office, at home, or in an ambulatory setting during the day.
Recent guidelines for detecting and managing hypertension recommend timely drug therapy if blood pressure stays at or above 130/80 mm Hg after 3-6 months of lifestyle changes.
Khashayar Hematpour, MD, a cardiologist and associate professor of the electrophysiology division at UTHealth Houston, who was not involved in the study, said the study confirms that at least two measurement techniques are needed to establish blood pressure, including a secondary method outside of the standard office setting.
“Doctors who deal with hypertension all the time — cardiologists, internists, primary care doctors — already know you don’t diagnose and treat hypertension based on one or two readings in the office,” Hematpour said.
Cheng said he and his colleagues are soon launching a randomized controlled trial of the clinical effectiveness of various methods for detecting and managing hypertension.
This study was supported by the Taiwan Ministry of Health and Welfare, the National Yang Ming Chiao Tung University, and the Taiwan Ministry of Science and Technology.
The study authors, Hematpour, McEvoy, and Murphy, reported having no relevant conflicts of interest.