Normal blood pressure (BP) is defined as systolic BP (SBP) < 120 mm Hg and diastolic BP (DBP) < 80 mm Hg.1 The thresholds for hypertension (HTN) are shown in TABLE 1.1 These thresholds must be met on at least 2 separate occasions to merit a diagnosis of HTN.1
Given the high prevalence of HTN and its associated comorbidities, the US Preventive Services Task Force (USPSTF) recently reaffirmed its recommendation that every adult be screened for HTN, regardless of risk factors.2 Patients 40 years of age and older and those with risk factors (obesity, family history of HTN, diabetes) should have their BP checked at least annually. Individuals ages 18 to 39 years without risk factors who are initially normotensive should be rescreened within 3 to 5 years.2
Patients are most commonly screened for HTN in the outpatient setting. However, office BP measurements may be inaccurate and are of limited diagnostic utility when taken as a single reading.1,3,4 As will be described later, office BP measurements are subject to multiple sources of error that can result in a mean underestimation of 24 mm Hg to a mean overestimation of 33 mm Hg for SBP, and a mean underestimation of 14 mm Hg to a mean overestimation of 23 mm Hg for DBP.4
Differences to this degree between true BP and measured BP can have important implications for the diagnosis, surveillance, and management of HTN. To diminish this potential for error, the American Heart Association HTN guideline and USPSTF recommendation advise clinicians to obtain out-of-office BP measurements to confirm a diagnosis of HTN before initiating treatment.1,2 The preferred methods for out-of-office BP assessment are home BP monitoring (HBPM) and 24-hour ambulatory BP monitoring (ABPM).
Limitations of office BP measurement
Multiple sources of error can lead to wide variability in the measurement of office BP, whether taken via the traditional sphygmomanometer auscultatory approach or with an oscillometric monitor.1,4 Measurement error can be patient related (eg, talking during the reading, or eating or using tobacco prior to measurement), device related (eg, device has not been calibrated or validated), or procedure related (eg, miscuffing, improper patient positioning).
Although use of validated oscillometric monitors eliminates some sources of error such as terminal digit bias, rapid cuff deflation, and missed Korotkoff sounds, their use does not eliminate other sources of error. For example, a patient’s use of tobacco 30 to 60 minutes prior to measurement can raise SBP by 2.8 to 25 mm Hg and DBP 2 to 18 mm Hg.4 Having a full bladder can elevate SBP by 4.2 to 33 mm Hg and DBP by 2.8 to 18.5 mm Hg.4 If the patient is talking during measurement, is crossing one leg over the opposite knee, or has an unsupported arm below the level of the heart, SBP and DBP can rise, respectively, by an estimated mean 2 to 23 mm Hg and 2 to 14 mm Hg.4
Although many sources of BP measurement error can be reduced or eliminated through standardization of technique across office staff, some sources of inaccuracy will persist. Even if all variables are optimized, relying solely on office BP monitoring will still misclassify BP phenotypes, which require out-of-office BP assessments.1,3FIGURE 1 reviews key tips for maximizing the accuracy of BP measurement, regardless of where the measurement is done.
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