Confirmation or exclusion of stage I hypertension by ambulatory blood pressure monitoring

Criteria for the diagnosis or exclusion of hypertension using ambulatory blood pressure monitoring have not been agreed upon. We designed this study to provide a statistically based guide for using results of ambulatory blood pressure monitoring to resolve this issue. To generate this information, we used a database of 228 subjects (135 men, 93 women; average age, 45 years) referred by their primary physicians over the past 7 years for evaluation of borderline or stage I hypertension (average blood pressure, 148/92 mm Hg; SD, ± 17.5/12.2 mm Hg). In this population, the pooled SDs of systolic and diastolic ambulatory blood pressures were 13.8 and 11.6 mm Hg, respectively. Using the pooled SD, we calculated the probability that a patient's blood pressure falls within the hypertensive range (>140/90 mm Hg). The 95% confidence interval for each subject's blood pressure was also determined. For example, if 40 ambulatory blood pressure measurements are performed on a subject and the average systolic ambulatory blood pressure is 137 mm Hg, then there is a 10% probability that the patient's 'true' average blood pressure is actually in the hypertensive range. By contrast, if the systolic pressure is 143 mm Hg, there is a 90% probability that the patient is hypertensive. This approach may be useful for clinical decision making and also for the design of clinical trials.