Manual or automated sphygmomanometer? A historical cohort to quantify measurement bias in blood pressure recording.

The authors aimed to quantify end-digit and threshold biases in blood pressure (BP) measurement with manual and digital sphygmomanometers. In a 3-year follow-up, end-digit and threshold biases were investigated and a new index, called the deviation index, was used to quantify measurement bias. The distribution of systolic and diastolic BPs became close to normal after implementation of digital sphygmomanometers. The appearance of zero end digits decreased from 97% to 30% (P<.0001). The deviation index decreased from 97% to 20% (P<.0001). Mean systolic and diastolic BPs increased immediately after implementation of automated sphygmomanometers (124.22±0.83 vs 132.90±0.78 and 74.38±0.50 vs 80.43±0.51, respectively; P<.0001 for both) but showed a linear decreasing trend during follow-up (systolic -3.59 mm Hg per year; 95% confidence interval, -5.57 to -1.61 [P<.0001]; diastolic: -2.52 mm Hg per year; 95% confidence interval, -3.78 to -1.26 [P<.0001]). Threshold bias decreased from 12.94% to 6.68% (P<.0001). Replacing manual sphygmomanometers with digital devices decreased end-digit and threshold biases in BP measurement. The deviation index can be used to quantify the magnitude of measurement bias.