White-coat effect

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Practice Tip

In addition to identifying patients with white-coat effect, regular home BP monitoring may be a useful tool to increase patient adherence to the antihypertensive regimen.

 

Quick Tips

  • A patient is considered to be experiencing the white-coat effect when BP measured in the physician’s office is consistently higher than out-of-office BP measurements
  • 20%-30% of patients with hypertension may experience white-coat effect
    • In one small study, white-coat effect was observed in 62% of patients referred to a hypertension specialty clinic
  • Automated in-office BP readings can eliminate white-coat effect
  • Ambulatory BP monitoring and home BP monitoring may also be used to identify white-coat effect
  • Ongoing home BP monitoring may have the added benefit of improving adherence to the antihypertensive regimen

POP-observer-effect

Fifty consecutive patients referred to a specialist for the management of hypertension had their BPs measured using an automated device. The first measurement was taken with an observer in the room, followed by 5 consecutive readings with the patient alone in the room. White-coat effect was identified in 62% of patients.

Source: Myers MG. Blood Press Monit. 2006;11:59-62.

Why is this important?

White-coat effect is a common cause of elevated clinical BP readings, with a prevalence of 20%-30% among patients with hypertension.1 White-coat effect is often mistaken for treatment-resistant hypertension. In one recent study, 3 out of 8 patients with presumed treatment-resistant hypertension based on office BP values had normal ambulatory BP.2 Automated office BP or out-of-office BP measurements may be used to identify patients with white-coat effect.

Identifying patients with white-coat effect

In clinical practice, patients who are experiencing the white-coat effect—when BP measured in the physician’s office is consistently higher than out-of-office BP measurements—may be identified through use of automated office BP or out-of-office BP monitoring techniques.3,4

Automated office BP measurement (AOBP) may reduce patient anxiety, and also eliminates observer error. Devices are available that allow repeated BP measurements to be taken in the office setting in the absence of an observer. Recent studies have shown that 5 readings taken at 1-minute intervals, with the patient alone in a room, result in BP values comparable to mean awake ambulatory BP. AOBP is one method of ruling out the white-coat effect.3

Currently, there are 2 modalities that provide out-of-office BP measurements that are used in clinical practice: ambulatory BP monitoring (ABPM) and home BP monitoring.4 Both ABPM and home-BP monitoring can enhance the physician’s ability to detect the white-coat effect in patients with hypertension.

ABPM

At present, ABPM is the preferred method for detecting patients experiencing the white-coat effect.4 Ambulatory monitors are lightweight devices that are preprogrammed to take readings at preset intervals, usually every 15 to 30 minutes, throughout the day and night while patients go about their daily activities.4-6 The readings are downloaded into a computer in physicians’ offices and provide a full profile of the patient’s BP variability over a 24-hour period.

Because ABPM captures both daytime and nighttime BP readings, it can identify patients with nighttime BP elevations (nondipping BP pattern). There is evidence to suggest that failure of BP to decrease at night may be associated with increased risk for cardiovascular events.6 In addition, ABPM identifies patients with excessive morning surge who may also be at increased risk.6

The use of APBM may be limited in routine clinical practice in some regions because of the cost of ABPM devices,7 the need for trained clinic staff,7 insurance reimbursement issues and/or the availability of the technology.4 Although ABPM is not widely used in primary care practices, it is generally available in cardiovascular and hypertension centers.4

Home BP monitoring

Although ABPM is more accurate than home monitoring in ruling out white-coat effect, home BP measurement is a viable alternative. Home BP monitoring devices are extensively used in clinical practice, as they are readily available for purchase by patients, inexpensive, and offer a convenient way to monitor BP over long periods of time.4,5,7 Devices that measure BP using the upper arm are recommended. Wrist monitors are more prone to error, since the wrist must be held at heart level in order to obtain an accurate reading. However, wrist monitors may be the only viable alternative in patients with unusually large upper arms. Finger devices are not considered reliable.4,5

Patients should be trained in proper home BP measurement technique. Specifically, they should be instructed to take readings after resting for 5 minutes, while sitting with both feet flat on the floor, back supported, and arm supported at heart level. BP measurements should be taken in succession with a 1-minute interval between measurements.4

Patients should be counseled to record BP measurements for 7 days, with at least 2 morning and 2 evening measurements (prior to taking antihypertensive medications). In general, the average of all BP values (except the first day readings which should be discarded) should represent a reproducible home BP level that can be used for clinical decision making.4,7 One study has suggested that the average of as few as 6 home BP measurements provides an accurate measure of out-of-office BP.8

Several organizations, including the British Hypertension Society and the European Society of Hypertension, have developed protocols for the validation of home-BP monitoring devices, and it is important that only validated models be used.4,5,7 A listing of validated devices can be found at www.dableducational.org. While validated devices are generally accurate, there is some disagreement over the need to test device accuracy for individual patients.5,7 Individual monitors may be validated by comparison with readings taken using a mercury sphygmomanometer to detect substantial inaccuracies.5,7 This approach also presents a useful opportunity to provide training to the patient and monitor BP measurement technique.7

References

  1. Calhoun DA, Jones D, Textor S, et al. Circulation. 2008;117:e510-e526.
  2. De La Sierra, Segura J, Banegas J, et al. Hypertension. 2011;57:898-902.
  3. Myers M, Godwin M, Dawes M, Kiss A, Tobe S, Kaczorowski J. Hypertension. 2010;55:195-200.
  4. Pickering TG, White WB. J Am Soc Hypertens. 2008;2:119-124.
  5. Pickering TG, Hall JE, Appel LJ, et al. Hypertension. 2005;45:142-161.
  6. Pickering TG, Shimbo D, Haas D. N Engl J Med. 2006;354:2368-2374.
  7. Parati G, Stergiou GS, Asmar R, et al. J Hypertens. 2008;26:1505-1526.
  8. Chatellier G, Dutrey-Dupagne C, Vaur L, et al. Am J Hypertens. 1996;9:644-652.