How many measurements are necessary in diagnosing mild to moderate hypertension?

Objective. The aim of this study was to investigate how many blood pressure measurements are necessary in diagnosing mild to moderate hypertension. Methods. The subjects were 99 outpatients who were included on the basis of elevated diastolic (95 less than or equal to DBP less than or equal to 115 mmHg) and/or systolic (160 less than or equal to SBP less than or equal to 200 mmHg) blood pressure. After the initial measurement all patients underwent nine subsequent blood pressure measurements over a period of 7 months. None of the patients received antihypertensive drug treatment during the study. Results. Between the first (initial) and second measurements, there was a significant reduction in systolic (161.0 to 152.5 mmHg) and diastolic (101.5 to 97.1 mmHg) blood pressures (P < 0.01). The differences between pairs of subsequent measurements were not statistically significant. The average of the last five assessment sessions (two readings per session) was regarded as the 'conceptual average blood pressure'. Comparing the blood pressure at repeat measurement with the conceptual average blood pressure revealed misclassification in 19% of cases, even after four repeat measurements (threshold value 95 mmHg). Analysis of the subgroups (95 less than or equal to DBP < 105 mmHg and 105 less than or equal to DBP less than or equal to 115 mmHg) revealed that the proportion of misclassification greatly depended on the initial value and the accepted threshold value. At a threshold value of 95 mmHg, patients with 'high' initial diastolic blood pressure (105 less than or equal to DBP less than or equal to 115 mmHg) required only two repeat measurements (misclassification in 7% of cases after four repeat measurements). Of those with initial diastolic blood pressure values between 95 and 105 mmHg, 24% were misclassified after four repeat measurements. Conclusions. For these 'borderline' diastolic values, we propose larger numbers of measurements than are recommended in international guidelines. Our advice for values in this borderline region is to be reticent in starting antihypertensive drug treatment. The presence or absence of other cardiovascular risk factors should be taken into account when deciding whether treatment is required or not.