Clinical features, anthropometric characteristics, and racial influences on the 'white-coat effect' in a single-centre cohort of 1553 consecutive subjects undergoing routine ambulatory blood pressure monitoring.

BACKGROUND

Patients with high office blood pressures but relatively normal readings during daytime ambulatory monitoring have been the subject of much investigation and debate. This clinical finding in part depends on an alerting reaction to the circumstances of the clinical measurement, often described as the 'white-coat effect' (WCE). Little is known of the characteristics of patients that are associated with the white coat effect in a large population of routinely referred patients.

OBJECTIVE

To relate the size of the WCE (defined as the difference between office and ambulatory daytime readings) to clinical features that may influence this phenomenon.

METHODS

We categorized 1553 consecutive subjects (51.3% men, aged 17-88 years), who had been referred to a single centre for the assessment of suspected hypertension prospectively into three groups: those aged <40, 40-59, and >/=60 years.

RESULTS

WCE on systolic blood pressure (SBP) increased significantly with advancing age and was correlated positively to body mass index (BMI), age and treatment. We found significant correlations to sex (higher in women) and race. WCE on diastolic blood pressure (DBP) decreased slightly with advancing age and was correlated positively to BMI and significantly to race and sex. We found no correlation to age or treatment. Caucasians had a greater WCE than did non-Caucasians (P<0. 001 for SBP and DBP) and hypertensives had greater WCE than did normotensives (P<0.0001 for SBP and DBP). Multiple linear regression analysis showed that age and BMI are the most important factors influencing WCE on SBP and DBP.

CONCLUSIONS

Factors such as race, age and BMI may exert important influences on the size of WCE possibly via effects on sympathetic nervous system activity.