Clinic Blood Pressure Underestimates Ambulatory Blood Pressure in an Untreated Employer-Based US Population

Abstract

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: 45 ± 10.4 years) individuals (59% female, 7.4% African-American, 12% Hispanic) with screening BP <160/105 mmHg and not taking antihypertensive medication completed three 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 (LOESS) was used to model the relationship of the BP measures to age and BMI. The prevalence of discrepancies in ABP- vs CBP-defined hypertension status – white-coat hypertension and masked hypertension – were also examined. Results Average awake systolic/diastolic ABP (123.0/77.4 ± 10.3/7.4 mmHg) was significantly higher than the average of 9 CBP readings over 3 visits (116.0/75.4 ± 11.6/7.7 mmHg). aABP exceeded CBP by more than 10 mmHg much more frequently than CBP exceeded aABP. The difference (aABP>CBP) was most pronounced in young adults and those with normal body mass index (BMI). The systolic difference progressively diminished, though did not disappear, at older ages and higher BMIs. The diastolic difference vanished around age 65, and reversed (CBP>aABP) for BMI>32.5 kg/m2. While 5.3% of participants were hypertensive by CBP, 19.2% were hypertensive by aABP; 15.7% of those with non-elevated 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 non-elevated CBP have masked hypertension. Demonstrated CBP-aABP gradients, if confirmed in representative samples (e.g., NHANES), could provide guidance for primary care physicians as to when, for a given CBP, 24-hr ABP would be useful to identify or rule out masked hypertension.

Race and sex differences in ambulatory blood pressure measures among HIV+ adults

“…11, 25–27 Recent studies have suggested that men have higher awake BP and prevalence of masked hypertension. 28, 29 A higher prevalence of abnormal ABPM phenotypes among men may result from the higher prevalence of impaired sympathetic function and abnormal cardiac response to exercise, and lower estrogen levels, compared with women. 25, 30, 31 Previous research has suggested that the prevalence of masked hypertension may be higher in men than women.…”

Measuring arterial blood pressure in humans: Auscultatory and automatic measurement techniques for human biological field studies

“…To be consistent with The International Database on Ambulatory Blood Pressure Monitoring (IDACO), a minimum of 10 valid daytime readings are required to compute average awake ambulatory blood pressure and a minimum of 5 valid sleep readings are required to compute average sleep ambulatory blood pressure (Schwartz et al, 2016;Thijs et al, 2007).…”

“…If ambulatory monitoring is to be done in a field setting, depending upon the protocol, a researcher will need a lot of batteries (or fewer rechargeable batteries) to monitor a sufficient number of participants for study. It is advisable to use fully charged batteries for each measurement interval to be certain that data are not lost during the measurement period.To be consistent with The International Database on Ambulatory Blood Pressure Monitoring (IDACO), a minimum of 10 valid daytime readings are required to compute average awake ambulatory blood pressure and a minimum of 5 valid sleep readings are required to compute average sleep ambulatory blood pressure (Schwartz et al, 2016;Thijs et al, 2007). …”

Variable selection in the functional linear concurrent model

“…Hypertension diagnoses have historically been based solely on blood pressure measurements taken in the clinic setting, but a growing body of work demonstrates that out-of-clinic blood pressure provides a more complete assessment of cardiovascular health. Indeed, the term “masked hypertension” was coined to describe individuals with normal clinic blood pressure but elevated ambulatory or daytime blood pressure [22]; in the Masked Hypertension Study (888 subjects), 16% of participants with normal clinic blood pressure had masked hypertension [23]. …”

“…Previous analyses of ambulatory blood pressure have mostly focused on average daytime (or nighttime) blood pressure [24, 25, 23]. However, individual ambulatory blood pressure readings are thought to depend on the specific context at the time of measurement, which changes throughout the day.…”