Ambulatory Blood Pressure: Normality and Comparison With Other Measurements

To the Editor: Dr. Schettini and colleagues1 recently proposed that ambulatory blood pressure measurements are within the normotensive range if the 24-hour average is <125 mm Hg systolic and 80 mm Hg diastolic and if the daytime averages are <129 mm Hg and 84 mm Hg, respectively. These investigators also stated that more elevated limits of the ambulatory measurements would yield an artificially high prevalence of white coat hypertension.1 However, the opposite is true: higher thresholds for ambulatory blood pressure measurement would be associated with a lower prevalence of white coat hypertension.2 Schettini and colleagues determined normal ambulatory blood pressure limits as those that best correlated with 140/90 mm Hg on clinic measurement, using linear regression analysis. Several problems arise:1. The regression line provides the point estimate for predicting the population mean of the ambulatory blood pressure at any given level of clinic pressure. However, reference values should not be based on a predicted population mean but on the upper 95% confidence boundary around …