White coat effect (WCE) and white coat hypertension (WCH) are relatively prevalent in clinical situation (20 - 57% of WCH in the hypertensive population). The aim of this study was to analyze the determinant factors of WCE.

A prospective study was carried out in outpatient clinic in a consecutive hypertensives without receiving pharmacologic treatment. Twenty-four hour ambulatory blood pressure monitoring (ABPM) was performed following more than two resting blood pressure (BP) determinations carried out with the interval of 1 - 2 weeks by mercury sphygmomanometer. WCE was calculated for systolic and diastolic BP as the difference between a clinic BP (CBP) and an average daytime ambulatory BP (ABP). WCH was defined as;BP in the clinic ≥ 140/90 mmHg with a mean daytime BP by ABPM ≤137/≤89 mmHg.

1) Two hundred thirty-five patients (mean age 49.7 years, females 74%) were studied. Thirty-seven percent in male and forty-six percent in female patients fulfilled WCH criteria. 2) CBP was significantly correlated to daytime ABP (systolic BP;r=.47, p<.001 and diastolic BP;r=.65, p<.001). 3) The magnitude of WCE was greater in the group of WCH (28.9+14.6/19.3+6.9 mmHg) than ambulatory hypertensives (15.1+15.7/13.0+8.2 mmHg) (p<.001). 4) The magnitude of WCE is significantly correlated with female (r²=.12, p<.001) and the stage of CBP according to JNC-V (r²=.23, p<.001) in systolic BP, the stage (r²=.08, p<.001) in diastolic BP, and the stage (r²=.09, p<.001) and weight (r²=.15, p<.01) in mean BP.

The magnitude of WCE in essential hypertension diagnosed at the clinic is significantly correlated with female, the magnitude of clinic BP, and weight.