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Clinic Blood Pressure Underestimates Ambulatory Blood Pressure in an Untreated Employer-Based US Population: Results
Joseph E Schwartz1, Matthew M Burg2, Daichi Shimbo2
1From Center for Behavioral Cardiovascular Health (J.E.S., D.S., S.G., T.G.P.) and Department of Psychiatry (R.S.), Columbia University Medical Center, New York, NY; Department of Psychiatry and Behavioral Sciences, Stony Brook University, Stony Brook, NY (J.E.S., T.Y., S.G.); Department of Internal Medicine, Yale University School of Medicine, New Haven, CT (M.M.B.); USC Dornsife Center for Self-Report Science, University of Southern California, Los Angeles, CA (J.E.B., A.A.S.); and Department of Cardiology, Tokyo Metropolitan Geriatric Hospital and Institute of Gerontology, Tokyo, Japan (J.I.). joseph.schwartz@stonybrookmedicine.edu.
Insights
Ambulatory blood pressure (ABP) is often higher than clinic blood pressure (CBP), challenging the common belief it
Area of Science:
- Cardiology
- Hypertension Research
- Preventive Medicine
Background:
- Ambulatory blood pressure (ABP) is a superior predictor of cardiovascular risk compared to clinic blood pressure (CBP).
- A common misconception suggests ABP is typically lower than CBP.
- The relationship between CBP-ABP difference and age in the US population remained unexamined.
Purpose of the Study:
- To investigate the relationship between clinic blood pressure (CBP) and ambulatory blood pressure (ABP) in healthy US adults.
- To examine the age-related differences in the CBP-ABP gradient.
- To determine the prevalence of masked hypertension defined by ABP in individuals with normal CBP.
Main Methods:
- 888 healthy adults underwent 3 clinic BP assessments and 24-hour ABP monitoring.
- Comparison of CBP, awake ABP (aABP), and CBP-aABP difference across demographics.
- Locally weighted scatterplot smoothing modeled BP measures against age and BMI.
- Prevalence of white-coat and masked hypertension was assessed.
Main Results:
- Average awake ABP (123.0/77.4 mmHg) was higher than average CBP (116.0/75.4 mmHg).
- ABP exceeded CBP by >10 mmHg more frequently than vice versa, particularly in younger adults with normal BMI.
- Masked hypertension was identified in 15.7% of individuals with nonelevated CBP.
Conclusions:
- Contrary to popular belief, ABP is not consistently lower than CBP in healthy individuals.
- A significant portion of healthy individuals with normal CBP exhibit masked hypertension.
- Understanding CBP-aABP gradients can guide physicians in utilizing 24-hour ABP to diagnose masked hypertension.
Background:
Ambulatory blood pressure (ABP) is consistently superior to clinic blood pressure (CBP) as a predictor of cardiovascular morbidity and mortality risk. A common perception is that ABP is usually lower than CBP. The relationship of the CBP minus ABP difference to age has not been examined in the United States.
Methods:
Between 2005 and 2012, 888 healthy, employed, middle-aged (mean±SD age, 45±10.4 years) individuals (59% female, 7.4% black, 12% Hispanic) with screening BP <160/105 mm Hg and not taking antihypertensive medication completed 3 separate clinic BP assessments and a 24-hour ABP recording for the Masked Hypertension Study. The distributions of CBP, mean awake ABP (aABP), and the CBP-aABP difference in the full sample and by demographic characteristics were compared. Locally weighted scatterplot smoothing was used to model the relationship of the BP measures to age and body mass index. The prevalence of discrepancies in ABP- versus CBP-defined hypertension status-white-coat hypertension and masked hypertension-were also examined.
Results:
Average systolic/diastolic aABP (123.0/77.4±10.3/7.4 mm Hg) was significantly higher than the average of 9 CBP readings over 3 visits (116.0/75.4±11.6/7.7 mm Hg). aABP exceeded CBP by >10 mm Hg much more frequently than CBP exceeded aABP. The difference (aABP>CBP) was most pronounced in young adults and those with normal body mass index. The systolic difference progressively diminished, but did not disappear, at older ages and higher body mass indexes. The diastolic difference vanished around age 65 and reversed (CBP>aABP) for body mass index >32.5 kg/m2. Whereas 5.3% of participants were hypertensive by CBP, 19.2% were hypertensive by aABP; 15.7% of those with nonelevated CBP had masked hypertension.
Conclusions:
Contrary to a widely held belief, based primarily on cohort studies of patients with elevated CBP, ABP is not usually lower than CBP, at least not among healthy, employed individuals. Furthermore, a substantial proportion of otherwise healthy individuals with nonelevated CBP have masked hypertension. Demonstrated CBP-aABP gradients, if confirmed in representative samples (eg, NHANES [National Health and Nutrition Examination Survey]), could provide guidance for primary care physicians as to when, for a given CBP, 24-hour ABP would be useful to identify or rule out masked hypertension.
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