Wrist blood pressure self-measurement at home not always reliable, study indicates

Patients who self-measure their blood pressure at home using wrist devices may get inaccurate readings, according to a new study.

Researchers in Italy determined the difference in blood pressure measured at the upper arm and at the wrist under a doctor's supervision in the office and examined whether this difference was also present during self-measurement at home. Patients were trained to measure their blood pressure with both an upper-arm device and a wrist device. The wrist device was not equipped with a position sensor. For the upper-arm device, patients were instructed to bare their nondominant arm, rest in a sitting position for 5 minutes, apply the blood pressure cuff with appropriate position regarding the artery, keep their elbow on a desk and keep their forearm horizontal, and measure their blood pressure without moving from their seat. For the wrist device, they were instructed to use the same arm, keep their elbow on the desk and bend their forearm to place their wrist at heart level, and measure their blood pressure again without moving from their seat.

After training, each patient self-measured their upper-arm and wrist blood pressure, in that order, under a physician's supervision. Patients then measured their upper-arm and wrist blood pressure, in that order, at home every morning and every evening at the same time for 7 consecutive days. Systolic and diastolic values for arm and wrist were averaged separately to arrive at the values for data analysis. All patients also underwent cognitive assessment, including the Mini-Mental State Examination, at their initial visit. The goal of the study was to determine whether wrist measurement of blood pressure is performed reliably at home or if error is common. The reference measurement was defined as the difference between upper arm and wrist blood pressure detected in the office, and the home measurement error was defined as the discrepancy between office and home blood pressure differences. The study results were published online Aug. 22 by Hypertension.

A total of 721 patients from the general population were included in the study. Fifty-seven percent were women, and the mean age was 49.3 years. None had atrial fibrillation, and all had Mini-Mental State Examination scores above 25, indicating no clinical cognitive impairment. Systolic blood pressure was 2.5% lower when measured at the wrist than at the arm in the physician's office (P<0.002), while diastolic blood pressure showed no significant difference between measurement sites. At home, both systolic blood pressure (5.6%) and diastolic blood pressure (5.4%) were higher at the wrist than at the arm (P<0.0001 for both comparisons). Of the 721 patients, 621 had a home measurement error of at least ±5 mm Hg. Among this group, 508 had higher blood pressure measurements at the wrist than at the upper arm and 113 had lower blood pressure measurements at the wrist than at the upper arm. Four hundred fifty-five patients had a home measurement error of at least ±10 mm Hg. In multivariable regression analysis, the researchers found that lower praxic ability was linked to errors in both systolic and diastolic measurement. Worse memory with interference and forearm length were found to be predictors of systolic error, while performance on the clock drawing test was found to be a determinant of diastolic error.

The authors noted that they had no gold standard to establish the reliability of wrist self-measurement at home, that the home measurement error was assumed to be due to the wrist rather than the arm device, and that a random protocol for measurement was not used. However, they concluded that home self-measurement of blood pressure with wrist devices often leads to falsely elevated readings, presumably because of poor patient comprehension of instructions and resultant incorrect arm positioning.

“It is likely that many subjects, when left free to measure their [blood pressure] at home, did not follow the instructions received during the training session because of a deficit in memory or in executive functions, a limitation that persisted after adjustment for age and was not prevented by years of schooling,” the authors wrote, adding that the lack of accuracy in wrist measurement by a majority of patients is “alarming” since wrist devices have a large market share in many countries and patients often use them without receiving any training. They recommended that clinicians “discourage the use of wrist devices in patients in whom cognitive deterioration is likely to be present.”