Sources of Error in Office Blood Pressure Measurement

Roy N. Morcos, MD, FAAFP; Kimbroe J. Carter, MD; Frank Castro, MS; Sumira Koirala, MD; Deepti Sharma, MD; Haroon Syed, MD


J Am Board Fam Med. 2019;32(5):732-738. 

In This Article

Abstract and Introduction


Purposes: To evaluate 2 commonly overlooked sources of error in measuring blood pressure (BP) in the office, improper patient positioning and frequency of terminal digit bias (TDB) using manual and automated (BP) devices.

Methods: BPs recorded by 3 nurses using manual and automated devices were analyzed for TDB. In the next part of the study, 294 patients were recruited and tested with each patient's BP measured twice in the table position and compared with BP measured in the chair position. To eliminate concern for position sequence, a randomized controlled trial was initially conducted.

Results: Significant TDB for the digit zero was identified in BPs measured by all nurses using a manual device. No such bias was identified for any nurse when measuring BP with an automated device. For the positional study, the randomized controlled study showed no significant sequencing effect therefore the sequence of table then chair BP measurements was adopted. Significant BP lowering was observed in 128 patients (42.7%) in the chair compared with the table position. Misclassification of prehypertension and hypertension would have occurred in 15.3% and 16% of patients, respectively, when BP was recorded in the table instead of the chair position.

Conclusions: Significant TDB was identified for all nurses when using a manual but not an automated device. Patient positioning on the examination table resulted in elevations of systolic and diastolic BPs.


The prevalence of hypertension is increasing in the United States and worldwide, causing a significant burden of disease.[1] Hypertension doubles the risk of coronary heart disease, congestive heart failure, stroke, chronic kidney disease, and peripheral arterial disease. Among all risk factors, hypertension ranks first in disability-adjusted life-years worldwide.[2,3] The diagnosis of hypertension is based on indirect measurements of blood pressure (BP) using office, ambulatory, or home BP devices. Although the office BP measurement is not ideal, it is most commonly used to diagnose and monitor patients' responses to therapy. Most published trials of treatment recommendations are based on office BP measurements.[4,5]

BP measurements are subject to errors such as terminal digit bias (TDB)—an observer's preference for a last digit, usually zero, and a tendency to round up or down the BP measurement to that digit.[7,8] Another source of error is inappropriate patient positioning (eg, having the patient sit on an examination table instead of in a comfortable chair). An observational study[9] revealed that the recommended patient positioning in a chair was followed in only 10 of 25 primary care offices, and in the remaining, patients were seated on the examination table. A 5-minute rest period before measuring BP was allowed in only 10 of 25 offices, and an automated device was utilized in only 2 of 25 offices.

In a previous study using a manual (aneroid) device, we showed that such improper positioning resulted in misclassification of prehypertension and hypertension in 7.4% and 5.9% of patients, respectively.[9] Although the automated device is the preferred BP measurement method, manual aneroid devices continue to be used in medical offices.[8–12] Accurate and precise office BP measurement with manual or automated devices is essential to adequately diagnose and treat hypertension.

Proper patient positioning is emphasized in the medical literature, but we could not find the impact improper positioning has on misclassification of patients as having prehypertension or hypertension. The article studies 2 commonly overlooked sources of error in measuring BP in the office—the impact of improper patient positioning and frequency of TDB. The accuracy and reliability of such measurements is of utmost importance to provide the best possible patient care.