Ambulatory Blood Pressure vs Clinic Blood Pressure

Patients with elevated clinic blood pressure did not have lower ambulatory blood pressure (ABP), according to results from the Masked Hypertension Study published in Circulation.

A total of 2600 employees initially participated in the BP screenings conducted by researchers at Stony Brook University and Columbia University in New York. Ultimately, 1011 individuals were enrolled in the study and completed 1 visit; 904 had clinic BP assessed 3 separate times; 893 wore the ABP monitor; and 942 completed the cardiovascular evaluation at the fifth visit. The mean age was 45 years (59% female, 7.4% black, 12% Hispanic). These individuals were considered healthy and were not taking antihypertensive medications at the time of enrollment.

The researchers compared 888 participants against 123 who were also enrolled in the study but dropped out before finishing the ABP monitoring (n=118) or had fewer than 10 valid awake ABP (aABP) readings (n=5). They then compared the distributions of clinic BP, mean aABP, and the clinic BP–aABP difference in the full sample and by demographic characteristics.

The average systolic/diastolic awake ABP reading was significantly higher than the average of 9 clinic BP readings over 3 visits (123.0/77.4 mm Hg ± 10.3/7.4 mm Hg vs 116.0/75.4 mm Hg ± 11.6/7.7 mm Hg, respectively).  In addition, the aABP surpassed the clinic BP by more than 10 mmHg more often than the clinic BP surpassed the aABP reading. That difference was most noticeable in young adults and patients with normal body mass indices (BMI).

The researchers also examined clinic BP and aABP separately to get a better understanding of the clinic BP–aABP difference. They calculated the prevalence of BP phenotypes (sustained normotension, white coat hypertension, masked hypertension, and sustained hypertension) and used locally weighted scatterplot smoothing (LOESS) with iterative reweighting to model the relationship of BP measurements to age and BMI.

In the sample of participants who did not have stage 2 hypertension, were not on any antihypertensive medications, and were cardiovascular disease (CVD)-free, more than 5% were considered hypertensive by clinic BP assessment, more than 19% were considered hypertensive by aABP, and 15.7% of those with nonelevated clinic BP had masked hypertension. Meanwhile, sustained normotension was 79.8%, masked hypertension was 14.9%, white coat hypertension was 1.0%, and sustained hypertension was 4.3%.

When comparing differences by sex, race, ethnicity, and BMI, men had both higher clinic BP and aABP readings than women, blacks had higher BP than nonblacks (although not considered statistically significant), and those who were overweight or obese had higher BP than those with normal BMIs.

The researchers noted that their findings confirm that the clinic BP–aABP difference “varies systematically with age,” with the difference being most pronounced in younger individuals and tapering with older ages.

“In contrast to previous large cohort studies of patients with elevated [clinic BP] and thus to a widely held belief of clinicians, ABP is not usually lower than [clinic BP] in healthy, employed individuals,” they concluded. “Furthermore, a substantial number of otherwise healthy individuals have masked hypertension that may warrant treatment or at least monitoring.”

If confirmed in more diverse groups, these findings could advise primary care physicians as to when clinic BP dictates the need for ABP monitoring to uncover masked hypertension.

Study Limitations

• The study sample is not necessarily representative of the general population as all participants were employed with employer-provided health insurance. Therefore, there were very few individuals older than aged 65 years, which is typically the age group with the most hypertension.  
• Since none of the individuals in the study were taking antihypertensive medications, the clinic BP–aABP difference cannot be applied to those who are on those medications.
• No home BP monitoring was conducted, which means the results may not be relevant to the clinic BP–home BP difference or the prevalence and correlates of masked hypertension defined by home BP instead of aABP.

Reference

1. Schwartz JE, Burg MM, Shimbo D, et al. Clinic blood pressure underestimates ambulatory blood pressure in an untreated employer-based US population. Results from the Masked Hypertension Study. Circulation. 2016;134:1794-1807. doi:10.1161/CRICULATIONAHA.116.023404.

This article originally appeared on The Cardiology Advisor