Minimally sufficient numbers of measurements for validation of 24-hour blood pressure monitoring in chronic kidney disease

Ambulatory blood pressure monitoring (ABPM) remains a reference standard, but the minimal number of ABPM readings required to diagnose hypertension has not been empirically validated. Among 360 patients with chronic kidney disease and 38 healthy controls, 24-hour blood pressure was recorded 2 times per hour during the night and 3 times per hour during the day. All subjects had at least 90% of the expected readings recorded. From this full set of ABPM recordings, we selected variable numbers of measurements and compared the performance of the selected readings against that of the full sample under either random or sequential sampling schemes. With 8 randomly selected systolic blood pressure readings, we were able to make diagnostic decisions in concordance with that from the full ABPM sample 91.0% of the time (kappa 0.804). With 15 randomly selected diastolic blood pressure readings, we made concordant decisions 96.3% of the time (kappa 0.810). A serial selection scheme generally required a greater number of readings to achieve the same levels of concordance with the full ABPM data. With a random selection scheme, 26 readings provided 95% confidence that the sample mean will be within 5 mm Hg of the true systolic blood pressure mean, and within 3.5 mm Hg of the true diastolic blood pressure mean.