Blood pressure at the clinic, work and home. Are there white coats at work?

Background: Today there are mainly three methods for measuring blood pressure, namely by a health worker at the clinic, by self-monitoring (often called home monitoring) and ambulatory monitoring. These methods give different mean values. All present studies concerning the relation between high blood pressure and organ damage are based on blood pressure measurements at clinics, and therefore the predictive values of home and average 24-h ambulatory measurements are not known. Comparative studies on "white coat effect" on blood pressure in Iceland are lacking. Furthermore, the Icelandic people have long working days and therefore some knowledge on blood pressure at work is of interest. The relation between blood pressure at the clinic and at work is unknown Objective: To analyse possible white coat effects of blood pressure and to compare these measurements with blood pressure values at work. Material and methods: During 1993-1994, 84 males aged 25-65 years were allocated to the study from five health centres and two hypertension clinics. Self-measurements of blood pressure were performed on UA-751 Digital Blood pressure Meter at home, at work and at the clinic. All measurements were scheduled between 3 and 5 PM. For comparison with blood pressure at the clinical setting, the pressure was also measured by the doctor using conventional mercury sphygmomanometer. Three measurements were recorded at each place but only one each day. Results: Good correlation was found between mercury sphygmomanometer and automatic meter measured at the clinic when measured by standard correlation coefficients (r=0.9; p<0.001). Agreement analysis demonstrates however, more discrepancy between these two methods. Mean blood pressure is similar at the clinic and at work, but significantly higher than mean blood pressure at home (p<0.001 for both systolic blood pressure and diastolic blood pressure). Possible white coat (15%) and work related (12%) hypertension was observed. Conclusion: The mean blood pressure at work and in the clinic is similar and higher than that recorded at home. This strengthens the predictive value of clinical measurements and demonstrates the rise of blood pressure outside the home is not only due to a white coat effect. Self measurements at home can be useful to detect white coat phenomena. Comparison of self-measurements at work and at home can perhaps help to detect these effects. The agreement between the automatic blood pressure meter and the conventional mercury sphygmomanometer is unsatisfactory for clinical purposes and therefore the methods are not interchangeable.