Method of Measuring Blood Pressure Associated with Mean Levels

Thomas E. Kottke, MD, MSPH

New findings from a quality improvement study suggest the method of measuring blood pressure was associated with both mean blood pressure levels and the rate of hypertension diagnosis.

When compared with manual measuring, automated blood pressure measurement was linked to decreased terminal digital preference, but was not eliminated, and was additionally associated with significantly higher mean blood pressure levels.

“Although the tendency for manual blood pressure measurement to be inaccurate has been documented for decades and automated measurement has been shown to be accurate, we could not determine which method of measurement-–manual or automated—was more accurate in this study because we lacked an independent standard of measurement,” wrote study author Thomas E. Kottke, MD, MSPH, HealthPartners Institute.

Kottke and his institution implemented automated devices in favor of sphygmomanometer in all primary care clinics due to persisting terminal digit preference and beliefs that their use would lead to lower average blood pressure values.

For this study, investigators assessed the distribution of terminal digits, the distribution of blood pressure values, and the difference in mean values at 11 primary care clinics that converted to automated measurement in April 2012.

The analysis was built on values obtained from patients during the manual measurement period (April 2008 - March 2012) and the automated measurement period (May 2012 - April 2015). Maint outcomes were considered the distribution of terminal digitals and mean systolic blood pressure (SBP) values obtained during 4 years of manual measurement compared with 3 years of automated measurement.

In order to adjust for seasonal fluctuations in blood pressure level, investigators used a generalized linear mixed regression model with random intercept for clinic and adjusted for seasonal fluctuations, as well as patient demographic and clinical characteristics.

The study included a total of 1,541,227 blood pressure measurements from 225,504 unique patients. It consisted of 849,978 blood pressure measurements from 165,137 patients (mean age, 47.1 years; 58.2% female) during the manual measurement period and 691,249 measurements from 149,080 patients (mean age, 48.4 years; 56.3% female) during the automated measurement period.

Data show 23.4% of patients received a diagnosis of hypertension during the automated measurement period, compared to 19.1% of patients during manual measurement.

Investigators reported terminal digit preference and the preference to record certain SBP values were greater during the manual measurement period than during the automated measurement period.

Over the period of manual measurement, when the prevalence of each terminal digit was expected to be 20%, data show 32.8% of all terminal digits were 0. Then, during the automated measurement period, 12.4% of terminal digits were 0 instead of the expected 10%.

Moreover, the increase in the mean SBP value at the onset of the automated measurement period was 5.09 mm Hg (95% CI, 4.98 - 5.19 mm Hg), after covariate adjustment.

Investigators added that when stratified by season, the means of both SBP and diastolic blood pressure (DPB) were lowest in summer and highest in winter.

Additionally, fewer values recorded during the automated measuring period were below 140/90 mm Hg, compared with the manual measurement period (69.9% vs 84.3%; difference, -14.5%).

The study, “Association of an Automated Blood Pressure Measurement Quality Improvement Program With Terminal Digit Preference and Recorded Mean Blood Pressure in 11 Clinics,” was published in JAMA Network Open.