Comparison of nurse- and physician-determined clinic blood pressure levels in patients referred to a hypertension clinic: implications for subsequent management.

BACKGROUND

When measuring BP, the physician induces a transient pressor response triggered by an alarm reaction. This 'white-coat effect' can influence therapeutic decisions. Whether it depends on the characteristics of the physician has not been evaluated.

OBJECTIVE

To assess the 'white-coat effect' induced by several physicians in a large sample of patients, using the blood pressure measured by trained nurses as a reference.

SETTING

Referral hypertension clinic.

METHODS

Patients were selected for the study if they had been referred for the first time to the clinic and if they had had their supine systolic/diastolic blood pressure measured by a trained nurse (mean of the last two of three measurements taken every 1 min by an oscillometric device) and a physician (auscultatory method using a standard mercury sphygmomanometer). Physicians were included in the study provided they had seen at least 25 patients during the study period. The between-physician difference was assessed using linear regression analysis. Physician blood pressure was the dependent and nurse blood pressure was the independent variable.

RESULTS

From 1 January 1997 to 15 September 1997, 1062 patients (50% male, aged 52 +/- 14 years), seen by 10 physicians (26-187 patients per physician) and one nurse were included for analysis. The mean systolic/diastolic blood pressure for physicians was 162 +/- 27/ 97 +/- 15 mmHg and that for the nurse was 155 +/- 24/ 88 +/- 14 mmHg. The nurse-physician differences were -6 mmHg (range -67 to +66) for systolic and -8 mmHg (-44 to +31) for diastolic blood pressures. Major differences were observed between individual physicians. Intercepts of the physician blood pressure versus nurse blood pressure relationship ranged from 0.1 -60.7 mmHg for systolic and from 13.3-55.3 mmHg for diastolic pressures. The slopes of this relationship differed less between physicians for systolic (0.72-1) than for diastolic pressures (0.56-0.97). There was no difference between the patients seen by physicians in patients' age, sex, tobacco consumption, anti-hypertensive treatment or target-organ damage.

CONCLUSION

Large between-physician differences exist in the magnitude of the white-coat effect that cannot be explained by patient characteristics. Physicians should therefore not make any decisions based on blood pressure measured manually during a first encounter.