Proportion of US adults recommended out-of-clinic blood pressure monitoring according to the 2017 American College of Cardiology / American Heart Association guideline

Abstract

The 2017 American College of Cardiology/American Heart Association (ACC/AHA) Blood Pressure (BP) Guideline recommends out-of-clinic BP monitoring to screen for white coat (WCH) and masked hypertension (MHT) among adults not taking antihypertensive medication and white coat effect (WCE) and masked uncontrolled hypertension (MUCH) among adults taking antihypertensive medication. We estimated the percentage of US adults meeting criteria for out-of-clinic BP monitoring by the ACC/AHA guideline using the 2011-2014 National Health and Nutrition Examination Survey (n=9,623). Among US adults not taking antihypertensive medication, 92.6% (95%CI 90.7%-94.1%) with systolic/diastolic BP (SBP/DBP)≥130/80 mmHg met criteria for out-of-clinic BP monitoring to screen for WCH and 32.8% (95%CI 30.4%-35.3%) with SBP/DBP<130/80 mmHg met criteria to screen for MHT. Criteria for out-of-clinic BP monitoring to screen for WCH were less often met at older age and did not differ by race/ethnicity or sex. The proportion meeting criteria for out-of-clinic BP monitoring to screen for MHT was higher at older age, among men versus women and non-Hispanic blacks and whites versus non-Hispanic Asians or Hispanics. Among US adults taking antihypertensive medication, 12.5% (95%CI 10.5%-14.9%) with SBP/DBP≥130/80 mmHg met criteria to screen for WCE and 57.4% (95%CI 52.7%-62.1%) with SBP/DBP<130/80 mmHg met criteria to screen for MUCH. Criteria for out-of-clinic BP monitoring to screen for WCE was more commonly met at older age and among non-Hispanic blacks than non-Hispanic whites and to screen for MUCH in older adults and men. In conclusion, approximately 103.8 million US adults (45.8%) met 2017 ACC/AHA BP guideline criteria for out-of-clinic BP monitoring.

Graphical Abstract

In prior studies, 10% to 20% of adults not taking antihypertensive medication with blood pressure (BP) in the hypertensive range when measured in a clinic setting had white coat hypertension, defined by non-hypertensive BP levels when measured outside of the clinic setting.¹ Also, 15% to 30% of adults not taking antihypertensive medication with non-hypertensive BP levels when measured in the clinic had masked hypertension, defined as BP in the hypertensive range when measured outside of the clinic setting.^{2, 3} The corresponding terms for those taking antihypertensive medication are white coat effect and masked uncontrolled hypertension.^4-6 Most prior studies suggest white coat hypertension and white coat effect are associated with either no or only a modest increased risk for cardiovascular disease (CVD) events compared with normotension (i.e., clinic and out-of-clinic BP not in the hypertension range).^{1, 7} In contrast, masked hypertension and masked uncontrolled hypertension have consistently been associated with a two times higher risk for CVD events compared with normotension.^{2, 3} Many recent BP guidelines and position papers recommend out-of-clinic BP monitoring with ambulatory BP monitoring (ABPM) or home BP monitoring (HBPM) to screen for these phenotypes and guide the decision to initiate or intensify antihypertensive medication.^{1, 6, 8-12}

In 2017, the American College of Cardiology/American Heart Association (ACC/AHA) Guideline for the Prevention, Detection, Evaluation and Management of High BP recommended out-of-clinic BP monitoring to confirm the diagnosis of hypertension based on measurements obtained in the clinic and to evaluate whether individuals taking antihypertensive medication achieved their BP goal.^{4, 5} Among adults not taking antihypertensive medication, screening for white coat hypertension is recommended for those with clinic systolic BP (SBP) between 130 mm Hg and 159 mm Hg or clinic diastolic BP (DBP) between 80 and 99 mm Hg and screening for masked hypertension among those with clinic SBP between 120 and 129 mm Hg or DBP between 75 and 79 mm Hg (Table 1).^{4, 5} Among adults taking antihypertensive medication, out-of-clinic BP monitoring is recommended to screen for white coat effect among those taking ≥3 classes of antihypertensive medication with clinic SBP between 130 mm Hg and 139 mm Hg or DBP between 80 mm Hg and 89 mm Hg and to screen for masked uncontrolled hypertension in those with clinic SBP < 130 mm Hg and DBP < 80 mm Hg and increased CVD risk or target organ damage.^{4, 5} We quantified the proportion and number of US adults who met the ACC/AHA guideline criteria for out-of-clinic BP monitoring using data from the US National Health and Nutrition Examination Survey (NHANES).

Table 1.

The 2017 American College of Cardiology / American Heart Association guideline recommendations for out-of-clinic blood pressure monitoring.

Antihypertensive medication use	Clinic BP level	To screen for:	Criteria for being recommended out-of-clinic BP monitoring
			Clinic blood pressure criteria	Additional criteria
No	SBP ≥ 130 mmHg or DBP ≥ 80 mm Hg	White coat hypertension	SBP: 130 to 159 mm Hg or DBP: 80 to 99 mm Hg*	None
	SBP < 130 mm Hg and DBP < 80 mm Hg	Masked hypertension	SBP: 120 to 129 mm Hg or DBP: 75 to 79 mm Hg†	None
Antihypertensive medication use	Clinic BP level	To screen for:	Criteria for being recommended out-of-clinic BP monitoring
			Clinic blood pressure criteria	Additional criteria
Yes	SBP ≥ 130 mmHg or DBP ≥ 80 mm Hg	White coat effect	SBP: 130 to 139 mm Hg or DBP: 80 to 89 mm Hg‡	Taking ≥ 3 classes ofantihypertensive medication
	SBP < 130 mm Hg and DBP < 80 mm Hg	Masked uncontrolled hypertension	None	High cardiovascular disease risk or target organ damage§

BP: blood pressure.

SBP: systolic blood pressure.

DBP: diastolic blood pressure.

^*The criteria also require clinic systolic blood pressure < 160 mm Hg and clinic diastolic blood pressure < 100 mm Hg.

^†The criteria also require clinic systolic blood pressure < 130 mm Hg and clinic diastolic blood pressure < 80 mm Hg.

^‡The criteria also require clinic systolic blood pressure < 140 mm Hg and clinic diastolic blood pressure < 90 mm Hg.

^§High cardiovascular disease risk or target organ damage was defined as 10-year predicted atherosclerotic cardiovascular disease risk ≥10% according to the Pooled Cohort risk equations or a history of cardiovascular disease (i.e., myocardial infarction, coronary heart disease, stroke or heart failure) or the presence of chronic kidney disease.

METHODS

Data used in the current study are available on the National Center for Health Statistics of the Center for Disease Control and Prevention website: https://wwwn.cdc.gov/nchs/nhanes/Default.aspx. Other study material is available from the corresponding author. The NHANES is a cross-sectional study conducted in two-year cycles by the National Center for Health Statistics of the Centers for Disease Control and Prevention.¹³ The current analysis pooled data from the NHANES 2011–2012 and 2013–2014 cycles to produce more stable prevalence estimates. Among NHANES participants who were ≥20 years old (n=10,907), we excluded those without three valid clinic SBP and DBP measurements (n=704) or missing information on self-reported antihypertensive medication use (n=13), age, sex, race, smoking, total and HDL-cholesterol, and diabetes (i.e., variables used to calculate 10-year predicted atherosclerotic CVD [ASCVD] risk with the Pooled Cohort risk equations; n=567) leaving 9,623 participants for analysis. The NHANES protocols were approved by the National Center for Health Statistics of the Centers for Disease Control and Prevention Institutional Review Board. All participants provided written informed consent.

Data collection

Self-reported information on age, race-ethnicity, sex, current cigarette smoking and a previous diagnosis of diabetes, coronary heart disease, myocardial infarction, stroke or heart failure was collected using standardized questionnaires. Diabetes was defined as a fasting serum glucose ≥126 mg/dL, non-fasting serum glucose ≥200 mg/dL, hemoglobin A1c ≥6.5% or self-report of a history of diabetes with concurrent glucose-lowering medication use. Chronic kidney disease (CKD) was defined as an estimated glomerular filtration rate <60 ml/min/1.73 m² or urinary albumin to urinary creatinine ratio >30 mg/g. Target organ damage was defined by the presence of CKD. History of CVD was defined as a prior diagnosis of myocardial infarction, coronary heart disease, stroke or heart failure. The Pooled Cohort risk equations were used to calculate 10-year predicted ASCVD risk among participants without a history of CVD.¹⁴ High CVD risk was defined by a history of CVD or a 10-year predicted ASCVD risk ≥10%.

BP measurement and antihypertensive medication use

Trained physicians measured BP three times at 30-second intervals during a single visit using an appropriately sized cuff and mercury sphygmomanometer. The three SBP and DBP measurements were averaged. Among those not taking antihypertensive medication, hypertensive BP levels were defined as SBP ≥130 mm Hg or DBP ≥80 mm Hg and non-hypertensive BP levels were defined as SBP <130 mm Hg and DBP <80 mm Hg.^{4, 5} The corresponding terms for those taking antihypertensive medication were uncontrolled and controlled BP. Participants were considered to be taking antihypertensive medication if they responded yes to both of the following questions “Have you ever been told by a doctor or other healthcare professional that you had hypertension, also called high BP?” and “Are you now taking prescribed medication for high BP?” Drug names for antihypertensive medications recorded on the medication inventory were coded into classes based on their generic equivalents. Apparent treatment resistant hypertension was defined as SBP ≥130 mm Hg or DBP ≥80 mm Hg while taking three or more classes of antihypertensive medication or the use of four or more classes of antihypertensive medication regardless of BP levels.^{4, 5}

Recommendations for out-of-clinic BP monitoring

Out-of-clinic BP monitoring is recommended in the 2017 ACC/AHA guideline to identify the presence of white coat hypertension and masked hypertension among adults not taking antihypertensive medication and white coat effect and masked uncontrolled hypertension among adults taking antihypertensive medication (Table 1).^{4, 5}

Statistical Analysis

All analyses were conducted for participants not taking and taking antihypertensive medication, separately. Summary statistics were calculated for US adults with SBP/DBP ≥130/80 mm Hg and SBP/DBP <130/80 mm Hg, separately. We also estimated the percentage and number of US adults with SBP/DBP ≥130/80 mm Hg and SBP/DBP <130/80 mm Hg, separately, who met criteria for out-of-clinic BP monitoring, overall and within strata defined by age group (20 to 39, 40 to 59, 60 to 74 and ≥75 years), race-ethnicity (non-Hispanic white, non-Hispanic black, non-Hispanic Asian and Hispanic), sex, diabetes, CKD, history of CVD, 10-year predicted ASCVD risk (<5%, 5% to <10%, 10% to <20% and ≥20%) among those without a history of CVD, and high CVD risk or target organ damage. We calculated prevalence ratios for meeting criteria for out-of-clinic BP monitoring associated with each characteristic listed above using Poisson regression with robust variance estimators and adjustment for age group, race-ethnicity and sex. Among adults taking antihypertensive medication, we also calculated the prevalence and number of US adults meeting criteria for out-of-clinic BP monitoring and prevalence ratios for meeting the criteria by number of antihypertensive medication classes being taken and by apparent treatment resistant hypertension status.

All calculations applied the NHANES sampling weights to obtain nationally representative estimates. To account for participants with missing data, weights were recalibrated based on the proportion of NHANES participants excluded within strata defined by age, race-ethnicity, sex and NHANES cycle.^{15, 16} We conducted data management using SAS version 9.4 (SAS Institute, Cary, NC). The data analysis was performed using Stata V14 (Stata Corporation, College Station, TX).

RESULTS

US adults not taking antihypertensive medication

Among adults not taking antihypertensive medication, those with compared to without hypertensive BP levels were more likely to be ≥40 years old, non-Hispanic black, male and have diabetes, CKD, a history of CVD, 10-year predicted ASCVD risk ≥ 5% and high CVD risk or target organ damage (Table 2). Also, those with hypertensive BP levels were less likely to be Hispanic versus other race-ethnicity.

Table 2.

Characteristics of US adults ≥ 20 years of age not taking antihypertensive medication by clinic blood pressure level.

Characteristic	Clinic blood pressure
	Non-hypertensive (SBP < 130 mm Hg and DBP < 80 mm Hg)	Hypertensive (SBP ≥ 130 mm Hg or DBP ≥ 80 mm Hg)
	(n=4,941)	(n=2,095)
Age groups
20 to 39 years	53.4	27.0
40 to 59 years	34.9	45.7
60 to 74 years	9.3	20.4
≥ 75 years	2.4	6.8
Race/ethnicity
Non-Hispanic White	64.1	65.6
Non-Hispanic Black	9.5	12.6
Non-Hispanic Asian	6.1	5.2
Hispanic	17.5	13.4
Male	45.4	58.1
Diabetes	4.6	10.9
Chronic kidney disease	7.0	15.3
History of CVD*	3.0	4.8
10-year predicted ASCVD risk†
< 5%	84.6	56.8
5% to < 10%	9.0	17.5
10% to < 20%	4.1	14.6
≥ 20%	2.3	11.1
High CVD risk or target organ damage	14.3	36.6

SBP: systolic blood pressure.

DBP: diastolic blood pressure.

CVD: cardiovascular disease.

ASCVD: atherosclerotic cardiovascular disease.

Definitions of history of cardiovascular disease and high cardiovascular disease risk or target organ damage are provided in the methods section of the manuscript.

^†Calculated among adults without a history of cardiovascular disease (i.e., myocardial infarction, coronary heart disease, stroke or heart failure) using the Pooled Cohort risk equations.

Among adults not taking antihypertensive medication, 92.6% of those with hypertensive BP met criteria for out-of-clinic BP monitoring to screen for white coat hypertension and 32.8% of those with non-hypertensive BP met criteria to screen for masked hypertension (Table 3). Over 80% of US adults in every sub-group investigated met criteria for out-of-clinic BP monitoring to screen for white coat hypertension, except for those with a 10-year predicted ASCVD risk ≥20% wherein 71.6% met the criteria. The proportion of US adults meeting criteria for out-of-clinic BP monitoring to screen for masked hypertension was higher at older age, among non-Hispanic Blacks and Whites versus non-Hispanic Asians and Hispanics, men versus women and those with diabetes, higher 10-year predicted ASCVD risk and with versus without high CVD risk or target organ damage. Overall, 45.0 and 40.5 million US adults not taking antihypertensive medication met criteria for out-of-clinic BP monitoring to screen for white coat and masked hypertension, respectively (Table S1).

Table 3.

Percentage of US adults ≥ 20 years of age not taking antihypertensive medication who met criteria for out-of-clinic blood pressure monitoring by the 2017 ACC/AHA guideline.

Subgroup of US adults	Percentage (95% confidence interval) who met criteria to screen for:
	White coat hypertension	Masked hypertension
Overall	92.6 (90.7, 94.1)	32.8 (30.4, 35.3)
Age groups
20 to 39 years	96.0 (93.1, 97.7)	26.2 (23.9, 28.5)
40 to 59 years	93.6 (90.7., 95.6)	39.3 (34.6, 44.2)
60 to 74 years	89.2 (84.9, 92.4)	44.4 (37.8, 51.3)
≥ 75 years	82.6 (76.1, 87.7)	42.1 (32.8, 51.9)
Race/ethnicity
Non-Hispanic White	93.7 (90.9, 95.7)	34.6 (31.3, 37.9)
Non-Hispanic Black	89.2 (86.4, 91.6)	34.7 (31.4, 38.1)
Non-Hispanic Asian	89.8 (71.3, 94.2)	29.3 (25.6, 33.3)
Hispanic	92.8 (88.8, 95.4)	26.7 (23.4, 30.3)
Sex
Male	92.9 (90.5, 94.7)	40.3 (37.7, 42.9)
Female	92.2 (88.7, 94.7)	26.7 (23.8, 29.7)
No diabetes	93.0 (91.4, 94.3)	32.2 (29.6, 34.8)
Diabetes	89.3 (81.7, 93.9)	46.9 (38.8, 55.2)
No chronic kidney disease	94.4 (92.5, 95.9)	32.7 (30.2, 35.4)
Chronic kidney disease	82.5 (73.8, 88.8)	34.2 (26.9, 42.4)
No history of CVD	92.6 (90.7, 94.2)	32.8 (30.3, 35.5)
History of CVD	92.0 (80.6, 96.9)	32.9 (24.7, 42.3)
10-year predicted ASCVD risk†
<5%	97.0 (95.7, 97.8)	29.7 (27.2, 32.4)
5% to < 10%	95.0 (90.6, 97.4)	48.2 (43.0, 53.4)
10% to < 20%	89.0 (83.6, 92.7)	52.9 (43.7, 61.9)
≥ 20%	71.6 (64.0, 78.2)	51.9 (38.8, 64.7)
High CVD risk or target organ damage
No	97.2 (95.9, 98.1)	31.6 (28.9, 34.4)
Yes	84.7 (80.2, 88.3)	40.3 (35.1, 45.8)

CVD: cardiovascular disease.

ASCVD: atherosclerotic cardiovascular disease.

The criteria to screen for white coat hypertension and masked hypertension are presented in Table 1.

Definitions of history of cardiovascular disease and high cardiovascular disease risk or target organ damage are provided in the methods section of the manuscript.

^†Calculated among adults without a history of cardiovascular disease.

Factors associated with meeting the criteria to be screened for white coat hypertension and masked hypertension after age, race-ethnicity and sex adjustment are shown in Table S2.

US adults taking antihypertensive medication

Among US adults taking antihypertensive medication, those with uncontrolled BP were more likely to be ≥75 years old and non-Hispanic black, have CKD, a 10-year predicted ASCVD risk ≥20%, high CVD risk or target organ damage, to be taking one class of antihypertensive medication and have apparent treatment resistant hypertension compared to their counterparts with controlled BP (Table 4).

Table 4.

Characteristics of US adults ≥ 20 years of age taking antihypertensive medication by clinic blood pressure level.

Characteristic	Clinic blood pressure
	Controlled (SBP < 130 mm Hg and DBP < 80 mm Hg)	Uncontrolled (SBP ≥ 130 mm Hg or DBP ≥ 80 mm Hg)
	(n=1,099)	(n=1,488)
Age groups
20 to 39 years	6.7	5.1
40 to 59 years	41.3	30.9
60 to 74 years	38.5	40.0
≥ 75 years	13.4	24.0
Race/ethnicity
Non-Hispanic White	75.4	67.4
Non-Hispanic Black	11.8	17.5
Non-Hispanic Asian	2.7	4.0
Hispanic	8.2	9.2
Male	46.5	43.6
Diabetes	25.8	27.5
Chronic kidney disease	27.4	35.6
History of CVD*	21.4	22.4
10-year predicted ASCVD risk†
< 5%	36.6	19.9
5% to < 10%	26.2	16.8
10% to < 20%	24.6	25.9
≥ 20%	12.6	37.4
High CVD risk or target organ damage	57.5	76.3
Number of antihypertensive medication classes‡
1	34.1	41.8
2	43.6	33.8
3	15.0	16.8
≥ 4	7.3	7.7
Apparent treatment resistant hypertension	7.3	24.4

SBP: systolic blood pressure.

DBP: diastolic blood pressure.

CVD: cardiovascular disease.

ASCVD: atherosclerotic cardiovascular disease.

The criteria to screen for white coat effect and masked uncontrolled hypertension are presented in Table 1. The definitions of history of cardiovascular disease, high cardiovascular disease risk or target organ damage and apparent treatment resistant hypertension are provided in the methods section of the manuscript.

^†Calculated among adults without a history of cardiovascular disease.

^‡58 NHANES participants who reported taking antihypertensive medication but had no classes of antihypertensive medication identified during the pill bottle review were excluded from the analysis of number of antihypertensive medication classes and apparent treatment resistant hypertension.

Among US adults taking antihypertensive medication, 12.5% of those with uncontrolled BP met criteria for out-of-clinic BP monitoring to screen for white coat effect and 57.4% of those with controlled BP met criteria to screen for masked uncontrolled hypertension (Table 5). The proportion of those meeting criteria for out-of-clinic monitoring to screen for white coat effect was <20% in each subgroup of US adults, except among those taking three or four or more classes of antihypertensive medication and with apparent treatment resistant hypertension wherein the proportion was 52.4%, 52.5% and 52.4%, respectively. The proportion who met criteria for out-of-clinic BP monitoring to screen for masked uncontrolled hypertension increased across older age groups and was higher among men versus women, those with diabetes, CKD, history of CVD, higher 10-year predicted ASCVD risk, high CVD risk or target organ damage, taking more classes of antihypertensive medication and with versus without apparent treatment resistant hypertension. Overall, 3.7 and 14.7 million US adults taking antihypertensive medication met criteria for out-of-clinic BP monitoring to screen for white coat effect and masked uncontrolled hypertension, respectively (Table S3). Factors associated with meeting criteria to screen for white coat effect and masked uncontrolled hypertension after age, race-ethnicity and sex adjustment are presented in Table S4.

Table 5.

Percentage of US adults ≥ 20 years of age taking antihypertensive medication who met criteria for out-of-clinic blood pressure monitoring by the 2017 ACC/AHA high blood pressure guideline.

Subgroup of US adults	Percentage (95% confidence interval) of US adults who met criteria to screen for:
	White coat effect	Masked uncontrolled hypertension
Overall	12.5 (10.5, 14.9)	57.4 (52.7, 62.1)
Age groups
20 to 39 years	3.9 (1.1, 12.6)	19.8 (12.9, 29.2)
40 to 59 years	11.0 (7.7, 15.4)	32.6 (25.6, 40.5)
60 to 74 years	13.4 (10.7, 16.8)	75.9 (69.2, 81.5)
≥ 75 years	14.8 (10.5, 20.6)	100
Race/ethnicity
Non-Hispanic White	11.7 (9.0, 15.0)	56.0 (50.3, 61.6)
Non-Hispanic Black	18.2 (15.0, 21.8)	61.1 (53.3, 68.4)
Non-Hispanic Asian	6.5 (2.2, 26.9)	56.4 (46.4, 65.9)
Hispanic	11.4 (7.9, 16.1)	60.5 (53.2, 67.5)
Sex
Male	12.3 (9.7, 15.6)	66.4 (59.2, 73.0)
Female	12.7 (10.3, 15.6)	49.7 (44.2, 55.3)
No diabetes	10.1 (8.0, 12.6)	52.0 (46.5, 57.5)
Diabetes	19.0 (14.6, 24.5)	73.3 (64.5, 80.5)
No chronic kidney disease	12.0 (9.4, 15.0)	41.5 (36.5, 46.7)
Chronic kidney disease	13.5 (10.3, 17.6)	100
No history of CVD	10.5 (8.2, 13.4)	45.9 (40.6, 51.3)
History of CVD	19.5 (16.1, 23.5)	100
10-year predicted ASCVD risk†
< 5%	6.9 (3.2, 14.6)	11.3 (6.8, 18.3)
5% to < 10%	11.5 (6.2, 20.5)	17.3 (11.4, 25.2)
10% to < 20%	10.1 (6.4, 15.5)	100
≥ 20%	12.2 (8.4, 17.4)	100
High CVD risk or target organ damage∥
No	8.8 (5.2, 14.3)	0
Yes	13.7 (11.4, 16.3)	100
Number of antihypertensive medication classes‡
1	0	46.3 (39.7, 53.0)
2	0	52.6 (44.5, 60.5)
3	52.4 (44.0, 60.6)	80.3 (70.8, 87.2)
≥ 4	52.5 (41.8, 63.0)	91.6 (78.0, 97.1)
No apparent treatment resistant hypertension	0	54.7 (49.7, 59.6)
Apparent treatment resistant hypertension	52.4 (45.1, 59.6)	91.6 (78.0, 97.1)

CVD: cardiovascular disease, ASCVD: atherosclerotic cardiovascular disease.

The criteria to screen for white coat effect and masked uncontrolled hypertension are presented in Table 1.

Definitions of history of cardiovascular disease, high cardiovascular disease risk or target organ damage and apparent treatment resistant hypertension are provided in the methods section of the manuscript.

^†Calculated among adults without history of cardiovascular disease.

^‡58 NHANES participants who reported taking antihypertensive medication but had no classes of antihypertensive medication identified during the pill bottle review were excluded from the analysis of number of antihypertensive medication classes and apparent treatment resistant hypertension.

Overall, 45.8% (95% CI 43.9%, 47.8%) of US adults met criteria for out-of-clinic BP monitoring. Extrapolated to the US population, 103.8 (95% CI 94.0, 113.7) million US adults, 85.5 (95% CI 76.5, 94.5) million not taking and 18.3 (95% CI 16.0, 20.7) million taking antihypertensive medication, met criteria for out-of-clinic BP monitoring.

DISCUSSION

In the current study, almost all US adults not taking antihypertensive medication with BP in the hypertension range in a clinic setting and almost one-third of those without BP in the hypertension range when measured in a clinic setting met the 2017 ACC/AHA BP guideline criteria for out-of-clinic BP monitoring to screen for white coat hypertension and masked hypertension, respectively. Also, among US adults taking antihypertensive medication, 12.5% of those with uncontrolled clinic BP and over 50% of those with controlled clinic BP met criteria for out-of-clinic BP monitoring to screen for white coat effect and masked uncontrolled hypertension, respectively. Overall, an estimated 103.9 million US adults, 85.5 million not taking and 18.4 million taking antihypertensive medication, met criteria for out-of-clinic BP monitoring.

The association between white coat hypertension and CVD has been inconsistent in prior studies. Compared with non-hypertensive BP in the clinic and outside of the clinic, white coat hypertension was associated with a higher incidence of CVD in a meta-analysis of 20,445 adults in eight studies (odds ratio: 1.38, 95% CI: 1.15–1.65), a modest non-statistically significant increased risk in a meta-analysis of 12 studies and 18,344 participants (odds ratio: 1.18, 95% CI: 0.99–1.41) and no difference in risk in a meta-analysis of eight studies with 7,961 participants (hazard ratio: 0.96, 95% CI: 0.65–1.42).^{7, 17, 18} These data suggest white coat hypertension may be associated with a modestly increased CVD risk. However, many participants with white coat hypertension in these studies may have initiated antihypertensive medication during follow-up. This would lower their clinic BP, out-of-clinic BP and risk for CVD events. As a result, the association between white coat hypertension and CVD would appear weaker than if patients had not initiated antihypertensive medication based on their clinic BP. Economic modeling studies have shown cost-savings of out-of-clinic BP monitoring with ambulatory blood pressure monitoring to confirm the diagnosis of hypertension prior to initiating antihypertensive medication.^{19, 20} These studies support the 2017 ACC/AHA BP guideline recommendation to use out-of-clinic BP monitoring to confirm the diagnosis of hypertension and rule out white coat hypertension.^{10, 21-23}

It has been estimated that 15% to 30% of adults have masked hypertension and it is associated with a two times higher risk for CVD.^{3, 18, 24} Therefore, the population attributable risk for CVD associated with masked hypertension may be high. The 2017 ACC/AHA BP guideline provides a Class IIa recommendation to initiate antihypertensive medication in adults with masked hypertension.^{4, 5, 25, 26} The results reported herein demonstrate that a substantial proportion of US adults without hypertension based on clinic BP measurements should be screened with out-of-clinic monitoring to detect masked hypertension. This approach may identify a large group of US adults who would receive substantial CVD risk reduction benefit from initiating antihypertensive medication.

Less than 20% of US adults were recommended out-of-clinic BP monitoring to screen for white coat effect. In a meta-analysis of 21,336 adults from 12 studies, the odds ratio for CVD associated with white coat effect compared to controlled BP was 1.16 (95% confidence interval: 0.91–1.49).¹⁷ These data suggest that individuals with white coat effect may receive limited CVD risk reduction benefits from intensifying antihypertensive medication. Although out-of-clinic BP monitoring to detect the white coat effect is not widely recommended by the 2017 ACC/AHA BP guideline, routine HBPM may be an efficient approach for facilitating BP control in patients taking antihypertensive medication, especially when used with other interventions (e.g., education, lifestyle counselling).^{27, 28}

The majority of US adults with controlled clinic BP while taking antihypertensive medication have high CVD risk or target organ damage and were recommended out-of-clinic BP monitoring by the 2017 ACC/AHA guideline to screen for masked uncontrolled hypertension. The excess CVD risk associated with masked uncontrolled hypertension versus controlled BP was demonstrated in a meta-analysis of 30,652 participants from 11 prospective studies that reported a hazard ratio of 1.80 (95% CI: 1.57–2.06).²⁹ While several guidelines recommend using clinic and out-of-clinic BP monitoring to evaluate BP control, the CVD risk reduction benefits associated with using out-of-clinic compared with clinic BP measurement to guide antihypertensive medication intensification has not been reported from a large outcomes trial.^{30, 31} The Masked uncontrolled hypertension Management Based on Office BP or on Out-of-office (Ambulatory) BP Measurement trial has begun enrolling participants and may provide information on the value of using out-of-clinic BP to guide antihypertensive treatment intensity.³²

A high percentage of all sub-groups investigated were recommended screening for white coat hypertension while a small percentage of almost all groups was recommended to be screened for white coat effect. The one exception was that over 50% of US adults taking 3 or more classes of antihypertensive medication were recommended to be screened for white coat effect. Additionally, out-of-clinic BP monitoring to screen for masked hypertension and masked uncontrolled hypertension was more commonly recommended for higher risk population sub-groups including older adults and those with diabetes and a higher 10-year predicted ASCVD risk. Given the high CVD risk associated with masked hypertension and masked uncontrolled hypertension, it seems appropriate to direct out-of-clinic BP monitoring towards populations with high CVD risk.

Barriers to the widespread use of out-of-clinic BP monitoring need to be addressed for the 2017 ACC/AHA BP guideline recommendations for out-of-clinic BP monitoring to be fully implemented. Limited access, low procedure reimbursement, and patients’ lack of willingness and inability to successfully complete ABPM have been reported by primary care providers as major barriers to conducting the procedure.³³ Patient compliance, accuracy of the results, out-of-pocket costs of the device and time needed to instruct patients on the procedure have been identified as major barriers to performing HBPM.³³ Strategies for increasing the use of out-of-clinic BP monitoring will require overcoming these barriers. This could include increasing reimbursement for ABPM and providing validated HBPM devices to patients at a reduced or no cost. Additionally, implementing programs aimed at training staff and patients in the use of ABPM and HBPM may be useful for increasing the use of out-of-clinic BP monitoring. Studies are needed to evaluate whether these approaches increase the guideline-recommended use of ABPM and HBPM.

The current study has several strengths. The sampling strategy used in NHANES allows for calculating nationally representative estimates for US adults in the overall population and within many population subgroups. NHANES uses rigorous data collection procedures including staff training and standardized protocols. There are also some potential limitations. The 2017 ACC/AHA BP guideline recommends calculating mean BP over multiple clinic visits, but NHANES measured BP during a single visit. Also, BP was measured by a physician in NHANES, which may have resulted in higher BP levels compared with measurements taken by a nurse or a medical technician.^{34, 35} Some NHANES participants may have been misclassified as having hypertensive-level BP, leading to the over-estimation of the absolute number of US adults being recommended out-of-clinic BP monitoring for white coat hypertension or white coat effect and under-estimation of the number recommended out-of-clinic BP monitoring for masked hypertension and masked uncontrolled hypertension. Left ventricular hypertrophy, a measure of target organ damage, was not available since echocardiograms were not performed in NHANES. Therefore, we may have underestimated the number of US adults with target organ damage, who would be recommended out-of-clinic BP monitoring to screen for masked uncontrolled hypertension. Finally, the sensitivity, specificity and predictive values of the criteria for out-of-clinic BP monitoring could not be evaluated since NHANES did not perform ABPM or HBPM.

Perspectives

In conclusion, the 2017 ACC/AHA BP guideline recommends out-of-clinic BP monitoring for a high proportion of US adults. The proportion who met criteria for out-of-clinic BP monitoring was highest to screen for white coat hypertension followed by masked uncontrolled hypertension, masked hypertension and white coat effect. These data demonstrate the 2017 ACC/AHA BP guideline has the potential to increase the appropriate diagnosis of hypertension through the widespread use of out-of-clinic BP monitoring.

Novelty and Significance:

1). What Is New?

• Approximately 103.8 million US adults (45.8%) of US adults met criteria for out-of-clinic blood pressure monitoring in the 2017 American College of Cardiology/American Heart Association blood pressure guideline.

• A high percentage are recommended out-of-clinic blood pressure monitoring to screen for white coat hypertension, masked hypertension and masked uncontrolled hypertension.

2). What Is Relevant?

• The 2017 American College of Cardiology/American Heart Association provided criteria to guide out-of-clinic blood pressure monitoring.

Summary

• A high percentage of US adults meet 2017 American College of Cardiology/American Heart Association guideline criteria for out-of-clinic blood pressure monitoring.