Background: The negative white-coat effect (WCE), a phenomenon in which out-of-office blood pressure (BP) is higher than clinic BP, has not been well examined, unlike the WCE.
Methods: As part of the Jichi Morning Hypertension Research study, in which clinic and home BP were measured in 969 hypertensive outpatients, 405 patients with normal clinic BP were separately analyzed. Clinic BP was measured on two different occasions, and home BP was measured twice in the morning and twice in the evening for three consecutive days. Clinic and home BP were each averaged from all readings, and negative WCE was defined as clinic systolic BP (SBP) lower than home SBP.
Results: Negative WCE was observed in 324 (33%) of the patients overall and in 173 (42%) of the patients with controlled BP (clinic BP < 140/90 mm Hg). In multiple logistic regression analysis adjusting for covariates including home SBP and pulse rate, negative WCE was correlated with older age (odds ratio (OR) 1.03, 95% confidence interval (CI) 1.01-1.06) and male gender (OR 1.08, 95% CI 1.01-1.14) in overall subjects. Among patients with well-controlled clinic BP, negative WCE was significantly correlated with the presence of ischemic heart disease (OR 1.17, 95% CI 1.04-1.31). The association of negative WCE with age and male gender remained significant under stringent criteria (negative WCE < -10.2 mm Hg (the mean -1 s.d.)).
Conclusions: Negative WCE remaining even after clinic BP is controlled may be related to cardiovascular risk factors such as older age, male gender, and a history of ischemic heart disease.