Observer-related: Hearing deficit; terminal digit bias (ie, preference for rounding BP reading to a specific end digit, eg, 0); measurement of diastolic BP at Korotkoff phase IV rather than phase V.
Procedure-related: Patient’s body position (eg, standing vs supine; legs crossed at knee; unsupported back or arm; arm lower than heart level); incorrect size or placement of cuff; talking during measurement (the content of conversation may influence results); and reliance on a single BP measurement.
Equipment-related: Device model bias; device calibration error.
The USPSTF, the UK’s National Institute for Health and Clinical Excellence, and other groups endorse ambulatory BP monitoring as the optimal method for BP measurement.
As reported by Kallioinen et al9, the magnitude of these potential errors ranges from small to large in both the positive and negative direction for both systolic and diastolic BP, and several sources of error are potentially bidirectional. For example, talking during BP measurement may result in an increase in systolic BP of 4 to 19 mm Hg and in diastolic BP of 5 to 14.3 mm Hg; measurement of diastolic BP at Korotkoff phase IV rather than phase V significantly increases diastolic BP by 12.5 mm Hg; and recent alcohol intake can affect systolic BP by –23.6 to +24 mm Hg and diastolic BP by –14 to +16 mm Hg. Overall, the researchers found significant directional effects for 27 of the 29 potential sources of error, ranging from a mean –24 mm Hg to +33 mm Hg error for estimating systolic BP and a mean –14 mm Hg to +23 mm Hg for estimating diastolic BP.9
Careful adherence to guidelines ensures accurate BP measurement
Adequate training and standardized procedures can target and mitigate many of the identified sources of error; accordingly, all clinical staff responsible for obtaining a patient’s BP measurement should be trained not only in the correct method for accurate measurement but also in the identification of factors that may introduce errors.
