Isolated clinic hypertension presents a significant problem for physicians who rely on obtaining accurate clinic measures of blood pressure to render appropriate decisions regarding diagnosis and treatment.
When nurses or physicians measure and record their elevated blood pressures in the clinic, these patients are often diagnosed and treated for essential hypertension as their elevated clinic arterial pressures are presumed to be representative of their daily arterial pressures. This may or may not be true. Certainly, patients with established essential hypertension sustain elevated pressures throughout daily life, suggesting strong correspondence between their clinic and non-clinic blood pressure measures.
On the other hand, the correspondence between clinic and non-clinic blood pressures is quite poor for patients categorized as exhibiting isolated clinic hypertension. Unfortunately, isolated clinic hypertensive patients represent a significant proportion of adult patients identified in primary medical care settings as having high or borderline high blood pressure, with prevalence estimates ranging from 21 percent (Pickering et al., 1988) to 39 percent (Martinez et al., 1999).
The prevalence rate of isolated clinic hypertension has been reported to be even higher (44 percent) among children (Hornsby et al., 1991).
It is important to note that prevalence estimates of isolated clinic hypertension are somewhat lower in studies that employ multiple clinic visits than in studies that rely on a single clinic recording (Pearce et al., 1992), again confirming the importance of taking blood pressure measures across multiple clinic visits prior to diagnosis.
To further illustrate the importance of multiple clinic visits, Fogari et al. (1996) showed that the prevalence of isolated clinic hypertension in a sample of new hypertensive patients was quite different when calculated on the basis of a single clinic visit (25 percent isolated clinic hypertensive) or multiple clinic visits (14 percent isolated clinic hypertensive).
Although multiple clinic blood pressure determinations are recommended to rule out isolated clinic hypertension, there is evidence to suggest that many isolated clinic hypertensives continue to exhibit elevated blood pressure recordings even after several clinic visits (Fogari et al., 1996; Pickering, 1999 a).
Isolated clinic hypertension should be distinguished from what is called the ‘white coat’ effect. The white coat effect refers to the acute elevation in blood pressure in response to a clinic visit. In contrast to isolated clinic hypertension, the ‘white coat’ effect can be experienced by both normotensives and hypertensives alike. For example, a patient with normal daily blood pressures averaging 115/70 mm Hg might exhibit average blood pressures in the clinic of 125/80 mm Hg, a noticeable ‘white coat’ effect that does not compromise his or her categorization as a normotensive.
Likewise, an essential hypertensive patient may have an average clinic blood pressure of 160/100 mm Hg and a mean daily blood pressure of 150/95 mm Hg, both within the hypertensive range yet exhibiting a noticeable ‘white coat’ effect. Because evidence linking the acute ‘white coat’ effect to risk for either essential hypertension or cardiovascular disease is lacking (Lantleme et al., 2000), the remainder of this section will focus on the etiology and risk associated with isolated clinic hypertension.