"White coat" hypertension in the black female population

Catherine E. Cooke, PharmD, BCPS^*
Peter J. Carek, MD, MS
C. Wayne Weart, PharmD
Deborah S. Carson, PharmD

*Corresponding author for manuscript and reprint requests
e-mail: ccooke@pharmacy.ab.umd.edu
Author Information

Received: September 1997

Background.

The prevalence of white coat hypertension in the black female population has not been well defined. Black females constitute the majority of our patients. We performed a cross sectional study to determine the prevalence of white coat hypertension in these patients and to compare the cardiovascular risk profiles of those with white coat hypertension to those with sustained hypertension.

Methods.

Black females with an average office blood pressure of 140-160/90-105 mmHg wore 24-hour ambulatory blood pressure monitors (ABPM). Subjects with a >20mmHg systolic or >10mmHg diastolic difference between the average office blood pressure and the average awake blood pressure from the ABPM were labeled as white coat hypertensives. A cardiovascular risk profile ascertained whether each subject was obese, a current smoker, exercising fewer than twenty minutes three times a week, or has a total cholesterol level greater than 200 mg/dl, diabetes mellitus, or a positive family history for stroke or hypertension.

Results.

The prevalence of white coat hypertension was 38% and the average number of risk factors per patient for the white coat hypertensive group was 2.9. This result was similar to that for the sustained hypertensive group which had an average of 3.1 risk factors per patient.

Conclusion

White coat hypertension may be a common finding in black hypertensive females who have office blood pressure measurements of 140-160/90-105 mmHg.The cardiovascular risk profile of these white coat hypertensives was found to be very similar to that of sustained hypertensives. Key words. Hypertension; risk factors; cross-sectional studies

Patients with mild hypertension present a diagnostic dilemma. Many of them exhibit an elevated blood pressure in response to the stress of medical evaluation, a phenomena commonly called "white coat" hypertension. Ambulatory blood pressure monitoring has become the standard by which to establish a diagnosis of white coat hypertension in patients with casual blood pressures in the lower hypertensive range (diastolic blood pressure 90­105 mmHg).^1,2The prevalence of white coat hypertension in the black and female populations is currently not well known and its relationship to the development of sustained hypertension and subsequent cardiovascular disease is a subject of significant debate. Though the casual office blood pressure measurement by the physician leading to the diagnosis of hypertension has been linked epidemiologically to cardiovascular disease, ambulatory blood pressure monitoring has revealed that home blood pressure measurements are significantly lower than clinic blood pressures in individuals with borderline hypertension.^3,4 The average daily blood pressure has also been shown to predict cardiac end­organ damage.

It is not clear whether white coat hypertension presents the same cardiovascular risk as sustained hypertension. Theoretically, exclusion of individuals with white coat hypertension may provide evidence that sustained hypertension is an even greater predictor of subsequent morbidity and mortality from cardiovascular disease than previously believed. Furthermore, it is possible that treatment of white coat hypertension may not be necessary, thereby eliminating a number of individuals from unnecessary treatment and potential side effects.

In an attempt to provide some additional data regarding prevalence of white coat hypertension and associated risk factors, a cross-sectional study using 24-hour ambulatory blood pressure monitoring was performed. The objective was to determine the prevalence of white coat hypertension in the black female population and to compare the cardiovascular risk profile of subjects with white coat hypertension to subjects with sustained hypertension.

MATERIALS and METHODS

Subjects and Study Design

The study population was identified from a computer-generated inquiry of patients seen at the Medical University of South Carolina's Family Medicine Center after gaining project approval from the institutional review board. Specific parameters for this inquiry were established: black, female, aged 18-65 years, diagnosis of primary hypertension and blood pressure measurements in the range 140­160 mmHg systolic blood pressure (SBP) and 90­105 mmHg diastolic blood pressure (DBP) without pharmacologic intervention. Patients were excluded if they had a secondary cause of hypertension, peripheral vascular disease or coagulation disorder. Subjects were required to wear the ambulatory blood pressure monitor (ABPM) during a regular "work" day as subjects were not monitored on their days off.

Those patients meeting the above criteria were sent letters explaining the study. A follow-up telephone conversation requested their participation and established appointment times. Patients reported to the Family Medicine Center where they signed informed consent. Before the ABPM was placed on the subject, three seated blood pressure measurements were taken using a mercury column sphygmomanometer with a stethoscope for auscultation of Korotkoff sounds I and V, corresponding to SBP and DBP, respectively. Patients were eligible for ABPM placement only if their average SBP was 140­160 mmHg and their average DBP was 90-105 mmHg in the non-dominant arm (e.g. left arm of a right-handed person and vice versa) after sitting five minutes in a quiet room. After the three pre-monitor blood pressure measurements, patients were asked several questions about their risk factors for cardiovascular disease. Data was obtained on whether patients had diabetes mellitus, currently smoked, or exercised. Subjects were also interviewed about their family history of hypertension and stroke. Measurements were taken to obtain the patient's height and weight. Subjects were considered obese if their body mass index, BMI, was greater than 25 kg/m². ⁵ BMI was defined as the patient's weight (kg) divided by their height squared (m²). The total number of risk factors was determined for each patient. One point was given for each of the following positive risk factors: obesity, diabetes mellitus, current cigarette smoking, exercising less than 20 minutes three times per week, family history for either hypertension or stroke, and total cholesterol level greater than 200 mg/dl. The average number of risk factors for subjects in the white coat and sustained hypertensive groups was calculated. The Suntech AccuTracker II device was used for the ambulatory blood pressure monitoring.⁶ The blood pressure cuff was placed on the non-dominant arm. Calibration of the ABPM involved connecting a mercury column to the automated blood pressure cuff and comparing the results of manual blood pressure readings using a stethoscope to that of the ABPM. Blood pressure measurements were taken in the supine, sitting and standing positions and after two minutes of walking. At each test position, two readings were taken, three minutes apart. Five minutes were allowed between each test position. If the average of the differences between the ABPM and the manual reading was greater than 10 mmHg for the SBP and 5 mmHg for the DBP, the ABPM was returned to the company for repair. Calibration was performed before the start of the study and periodically thereafter.

The specifications for the ABPM were the same for all subjects. The maximum and minimum inflated cuff pressures were 240 mmHg and 40 mmHg, respectively. The blood pressure cuff deflated at a rate of 4 mmHg/sec. The display was turned off so subjects were unable to view the results of their blood pressure readings during the 24-hour monitoring period. The ABPM was set to inflate for blood pressure readings every 15 minutes while awake and every 30 minutes during sleep. The time periods for the awake and asleep hours were estimated by the subject. During blood pressure measurements, the ABPM also recorded heart rate (HR), and calculated mean arterial pressure (MAP) and pulse pressure (PP). The ABPM was also set to re-take blood pressure readings when certain criteria were met: SBP > 220 mmHg or < 80 mmHg, DBP > 130 mmHg or < 50 mmHg, HR > 120 beats/min, PP < 15 mmHg, or a deviation in the SBP > 25 mmHg, DBP > 25 mmHg or PP > 50 mmHg from the previous reading.

Patients were provided a log sheet to record the times they were awake, asleep, at work or exercising. The subjects wore the apparatus for 24 consecutive hours at which time they returned to the clinic for removal.

In terms of classification, patients with a difference of at least 20 mmHg SBP or 10 mmHg DBP from the average of the three office blood pressure measurements taken immediately prior to attachment of the ABPM to the patient minus the average awake ambulatory blood pressure (see Formula 1) were labeled as white coat hypertensives.^7-9 Those not meeting this definition were labeled as sustained hypertensives.

Formula 1 - White coat hypertension:
Avg. office BP - Avg. awake BP > 20 mmHg SBP or 10 mmHg DBP

Data Retrieval

The data on the ABPM was transferred to a computer database. AccuTrack software was used to facilitate data summary. Erroneous blood pressure readings were omitted. Criteria for erroneous readings were as follows:
1) pulse rate above 120 beats per minute,
2) systolic or diastolic blood pressure deviation exceeding 25 mmHg compared with the previous and the subsequent readings immediately before and after and
3) pulse pressure less than 15 mmHg.¹⁰
Patients were excluded if greater than 20% of their awake blood pressure readings were omitted.^10,11

The mean 24-hour blood pressure was determined. The times marking the beginning and end of the awake and asleep periods were obtained from the patient recorded log sheet. These times were used to categorize the blood pressure measurements into the awake or asleep periods and calculate the average awake and asleep blood pressure. Also, the 24 hour blood pressure load (percentage of SBP readings greater than 140 mmHg or DBP readings greater than 90 mmHg during the awake hours and/or 120 and 80 mmHg, respectively, during sleep) and the awake blood pressure load (percentage of readings greater than 140 and 90 mmHg for the SBP and DBP, respectively, during the awake period) were determined.¹²

RESULTS

The computer inquiry identified 645 patients who met the search specifications. Only 49 (7.6%) were not currently taking anti-hypertensive medications according to their prescription profile. Twenty-five (51%) of these patients consented to participate. Four subjects were excluded from the analysis. One subject was too large (> 160 kg) to properly fit a blood pressure cuff. One subject worked the night shift and two others had too few blood pressure measurements (i.e. >20% of the ABPM measurements were omitted). In four subjects, the batteries failed while they were asleep. These patients had data for greater than 90% of the awake period, but did not have complete data for the asleep period. These subjects were not included for the mean 24-hour blood pressure, mean asleep blood pressure, and average blood pressure load determinations.

Thirty eight percent (n=8) were found to have white coat hypertension and 62% (n=13) had sustained hypertension (Table I). These two groups had similar mean pre-monitor blood pressure averages. The average of the three pre-monitor DBP measurements minus the average awake DBP was greater than 10 mmHg in all subjects in the white coat group. Two of these subjects also had a SBP difference of 20 mmHg or more. However, meeting either of these criteria (a DBP difference greater than 10 mmHg or a SBP difference greater than 20 mmHg), was sufficient to categorize a subject as a white coat hypertensive.

Table I - Primary measures for hypertension classification

BP = blood pressure
Avg. = average

Both the mean 24-hour blood pressure and the mean asleep blood pressure average were lower for those with white coat hypertension (Table II). The average systolic and diastolic blood pressure loads for the 24-hour and the awake period were greater than 50% for the sustained group. This contrasts with the average systolic and diastolic blood pressure loads for the white coat group which were less than 27%.

Table II - Ancillary ABPM measures

^*White coat n=8, sustained n=13
BP = blood pressure
Avg. = average

The two groups were very similar with regards to their cardiovascular risk profile (Table III). The actual difference between the number of subjects in each category was very small. In both groups, the majority of subjects was obese, and did not exercise for a minimum of 20 minutes three times a week. Approximately one-fourth of the subjects with sustained hypertension and one-fourth of the subjects with white coat hypertension had diabetes mellitus. Fewer than 15% of subjects in both groups were current smokers. Twenty-five percent of subjects in the white coat group reported a family history of hypertension or positive family history for stroke in a first degree relative (mother, father, or siblings). Sustained hypertensive subjects reported a similar incidence of family history of hypertension (25%) but reported a slightly higher incidence of family history positive for stroke (46%). Forty percent of subjects in the white coat group and 50% of subjects in the sustained hypertensive group had cholesterol levels greater than 200 mg/dl. Data was not available on the total cholesterol level for every subject. Three subjects in each group had never been tested for total cholesterol at the Family Medicine Center and were not aware of their total cholesterol if they had been tested elsewhere.

Table III - Cardiovascular risk profile

^* white coat n=5, sustained n=10

The average number of risk factors per patient was 2.9 for the white coat hypertensive group and 3.1 for the sustained hypertensive group.

COMMENT

Hypertension has been shown to be associated with the development of coronary heart disease, stroke, and other cardiovascular disease.¹³ Approximately 60 million Americans have been diagnosed with hypertension based upon casual office blood pressures; 70­90% of these have "mild" hypertension (diastolic blood pressures 90­104 mmHg). Individuals with mild hypertension as determined by casual office blood pressure readings present a diagnostic dilemma, as many of these individuals may have only a transient rise in blood pressure.^14-16 This transient rise in blood pressure occurring in the medical setting defines white coat hypertension.

The percentage of the population with white coat hypertension has been reported to be between 15-40% for white males. Other groups, specifically black females, have not been studied. Our results indicate that 38% of black females with elevated clinic blood pressures at visits to the Family Medicine Center may have white coat hypertension. The relative increased prevalence found in our study appears logical as several studies have shown blacks to have a greater blood pressure reactivity to commonly used stressors. Furthermore, black hypertensives appear to be more susceptible to the pathophysiological consequences of an exaggerated blood pressure response to stress.^17,18

The clinical implications of white coat hypertension remain controversial. Sokolow and colleagues demonstrated a greater correlation between severity of hypertensive complications and the average ambulatory blood pressure reading taken over a two to three­day period compared with the average of three casual blood pressure readings.¹⁹ Evidence of target­organ damage (fundoscopic changes or left ventricular hypertrophy) was found in 64% of patients with sustained hypertension versus 19% in white coat hypertensives.¹⁴ Additionally, patients with blood pressure elevation only in the doctor's office have cardiac size and function similar to those of normotensive patients.²⁰ Several studies have shown the average daily blood pressure load rather than the 24­hour average blood pressure was better related to left ventricular mass index and left atrial index.²⁰ These results suggest that the percentage of readings in the hypertensive range may be a better predictor of future cardiac end­organ damage than either a single reading or the mean of numerous readings taken over a 24­hour period. If we used the average daily blood pressure load instead of the average awake blood pressure, the percentage of patients considered to have white coat hypertension would have been similar.

Julius and colleagues provided data that does not support the accepted practice of using home blood pressure determinations to distinguish groups of borderline hypertensive subjects with a lesser clinical problem.¹⁶ In their study of young subjects who were not taking any anti­hypertensive medications, both subjects with white coat and sustained hypertension were different from the normotensive group with regards to excessive risk of hypertension (past blood pressures, parental blood pressures, weight and heart rate) and excessive risk of atherosclerosis (triglycerides and insulin). Our study and that of Julius and colleagues supports the earlier finding by Devereus and colleagues who demonstrated that hypertensive cardiac hypertrophy appears to be more closely related to blood pressure during stressful situations than to basal blood pressure.²¹ This suggests that individuals with blood pressure elevations during stressful events should be considered to be very similar, if not the same, to those with sustained hypertension. Our present study confirms this observation. Does white coat hypertension present the same cardiovascular risk as sustained hypertension? If the answer is yes, then treating these patients with blood pressure lowering medications would be cost-effective. If the answer is no, the picture becomes more complicated. Is white coat hypertension a precursor to sustained hypertension? Should we use the "watch and wait" theory or begin treatment? How often should we monitor their blood pressure? What device should we use to monitor their blood pressure? Obviously, casual office measurements would give a misleading picture. Ambulatory blood pressure monitoring is the standard for diagnosing white coat hypertension, but cost is a factor. The charge for a 24-hour ambulatory blood pressure monitor study is approximately $100 to $150.

Currently, we do not know whether white coat hypertension is a significant risk factor for the development of cardiovascular disease or whether it is an inconsequential finding. When this question is answered, the risk to benefit ratio can be used to decide cost-effective management of patients with white coat hypertension.

CONCLUSION

Thirty-eight percent of black female subjects with elevated clinic blood pressures showed a decrease in blood pressure after leaving the Family Medicine Center and were labeled as white coat hypertensives. These subjects had "mild" hypertension, 140-160/90-105 mmHg, based on the average of three pre-monitor blood pressures measurements and were not on any anti-hypertensive medications. Their cardiovascular risk profile was similar to those subjects who were classified as sustained hypertensives.

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Institutional affiliation of all authors at time of study:

Medical University of South Carolina
Department of Family Medicine
295 Calhoun Street
Charleston, SC 29425, USA
phone (803) 792-2123
fax (803) 792-3598

Current affiliations:

Carek PJ, Weart CW, Carson DS Medical University of South Carolina Department of Family Medicine 295 Calhoun Street Charleston, SC 29425 tel (803) 792-2123 fax (803) 792-3598

Cooke CE University of Maryland School of Pharmacy Department of Pharmacy Practice and Science 100 Penn Street, Rm 216 Baltimore, MD 21201-1082 tel 410-706-8334 fax 410-706-4158 e-mail: ccooke@pharmacy.ab.umd.edu

 

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