Faculty Peer Reviewed
Hypertension is a pervasive chronic disease affecting approximately 65 million adults in the United States, and a significant cause of morbidity and mortality . Antihypertensives are widely prescribed due to their effectiveness in lowering blood pressure, thereby reducing the risk of cardiovascular events. However, the phenomenon of the “white coat effect” may be a complicating factor in the diagnosis and management of hypertensive patients. It is well established that a considerable number of people experience an elevation of their blood pressure in the office setting, and particularly when measured by a physician. The cause of this white coat hypertension, as well as its implications in the prognosis and treatment of hypertension, is still controversial.
The concept of white coat hypertension has existed for many years, with some of the first reports of blood pressure varying between a resting value and one taken by the physician written by Alam and Smirk in the 1930s . Studies since then have continued to demonstrate the elevating effect of a physician’s office on blood pressure, with an estimated 20% prevalence of white coat hypertension in the general population . The definition of white coat hypertension used in research continues to vary, however, producing a range of incidences from 14.7% to 59.6% . Most studies characterize white coat hypertension as an office blood pressure of greater than 140/90 mmHg, with ambulatory blood pressures less than 135/85 . The regular use of home blood pressure monitors and 24-hour ambulatory blood pressure monitoring (ABPM) has further demonstrated this discrepancy in clinical practice as well as in research.
White coat hypertension is hypothesized to be a result of anxiety and subsequent sympathic nervous system activation. Studies examining the presence of white coat hypertension among individuals with anxious traits have not found evidence of this association; rather it appears to be associated with a state of anxiety unique to the presence of a physician . In a study by Gerin, Ogedegbe, and colleagues, ABPM measurements of patients’ blood pressure in a separate laboratory facility were compared to ABPM measurements in the waiting room of a physician’s office and a manual blood pressure performed by a physician in the examining room. Their results demonstrated a significant elevation of blood pressure on the day of the physician’s office visit, with a larger increase in previously diagnosed hypertensive patients, and no difference in blood pressure between the waiting room and the examining room . This provides evidence for the notion that white coat hypertension is the result of a classically conditioned response to a physician’s office. That this occurred more often in patients with previously established hypertension may be due to an initial anxiety reaction as patients learn they have hypertension, which is further conditioned by the following office visits to check their blood pressure control .
The effect of isolated white coat hypertension on cardiovascular risk has been controversial. One study examining the target organ damage of hypertension in terms of left ventricular mass and carotid-femoral pulse wave velocity found a positive correlation with daytime blood pressure values, but not with those who had elevated office blood pressures alone . A recent meta-analysis likewise showed that cardiovascular risk is not significantly different between white coat hypertension and normotension . However, another study by Gustavsen and colleagues evaluating the rate of cardiovascular deaths and nonfatal events over a 10-year follow-up period found that patients with white coat hypertension and essential hypertension had similar event rates, but normotensive patients had significantly lower rates . In contrast, a different study determined that the unadjusted rate of all-cause mortality in patients with white coat hypertension (4.4 deaths per 1,000 years of follow-up) was less than patients with sustained hypertension (10.2 deaths per 1,000 years of follow-up), and that this was clinically significant after adjusting for age, sex, smoking, and use of antihypertensive medication . The effect of isolated white coat hypertension on cardiovascular risk still needs further investigation to determine the necessity of treating it with antihypertensives.
As hypertension is routinely diagnosed by the blood pressure measurements obtained by a physician in an office setting, it is likely that a significant portion of white coat hypertension is treated with antihypertensives. In the study by Gustavsen and colleagues, they noted that 60.3% of patients with white coat hypertension were treated with antihypertensives at some point during the 10-year follow-up . In the Treatment of Hypertension Based on Home or Office Blood Pressure (THOP) trial, antihypertensive treatment was adjusted based on either self-measured home blood pressure values or conventional office measurements. At the end of the 6-month period, less intensive drug treatment was used for the home blood pressure group as opposed to those measured in an office, and more home blood pressure patients could permanently stop antihypertensive drug treatment (25.6% vs. 11.3%). However, those treated based on home blood pressure measurements had slightly higher blood pressures at the end of the trial than those treated in the office, which could potentially increase cardiovascular risk . Evaluating whether a patient has sustained hypertension or white coat hypertension with normotensive ambulatory blood pressure using home devices or ABPM may help to identify those who do in fact require antihypertensive medications.
White coat hypertension may also play a role in cases of resistant hypertension. ABPM may be necessary to differentiate cases of true drug-resistant hypertension and those that are well controlled outside of the physician’s office in order to prevent overtreatment. One study found that when patients who were documented to have uncontrolled hypertension had their blood pressure monitored for 24 hours, only 69% were actually uncontrolled . Studies have also looked for other ways to differentiate true resistant hypertension and white-coat resistant hypertension, and have determined that true resistant hypertension patients have excessive intake of salt and alcohol as well as higher renin values .
In clinical practice, white coat hypertension is likely a common confounding factor in the diagnosis and treatment of hypertension. Patients often insist that their blood pressure is much lower at home than at their office visit, and the anxiety of an appointment solely for a blood pressure check is likely a contributing factor. Shifts away from physician measurement of blood pressure or substitution with automatic blood pressure devices may help to counteract this phenomenon. Home blood pressure monitoring devices can be a useful tool in discerning whether a patient’s blood pressure is properly controlled on a current treatment regimen or if additional therapy is needed. Avoiding overtreatment of hypertension may also lower health care costs, although the cardiovascular risks of white coat hypertension must be further elucidated so that the importance of treating white coat hypertension can be determined. White coat hypertension is a real and ubiquitous phenomenon, and must be considered by physicians for all patients with elevated blood pressures.
Commentary by Dr. Stephen Kayode Williams
Attending Physician, Bellevue Primary Care Hypertension Clinic
Are doctors bad for your blood pressure? Yes! This is a timely discussion as we eagerly await updated national guidelines for the management of hypertension. How will JNC 8 address this issue that comes up at every visit to our primary care clinics? The latest US hypertension guidelines were published in 2003 . The more recent 2011 UK guidelines are remarkable in stating that in order to confirm a new diagnosis of hypertension, ambulatory blood pressure monitoring (or alternatively home blood pressure monitoring) should demonstrate daytime blood pressures greater than or equal to 135/85 mmHg  . An exhaustive cost-effectiveness analysis performed for these guidelines came to the conclusion that, despite the expenses incurred with ambulatory blood pressure monitoring, there are vast cost savings that come with the prevention of an erroneous diagnosis of hypertension using office blood pressure readings alone. In this country, ambulatory blood pressure monitoring is not widely available in primary care. Stayed tuned to see how the upcoming hypertension guidelines address these clinical correlations.
Lauren Foster is a 4th year medical student at NYU School of Medicine
Peer reviewed by Stephen Kayode Williams, MD, MS, Bellevue Primary Care Hypersion Clinic
Image courtesy of Wikimedia Commons
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