Objectives: To assess the reproducibility of the circadian blood pressure (BP) pattern over a 48-h period by comparing the first 24 h of ambulatory blood pressure monitoring (ABPM) with the following 24 h and with the mean over 48 h.
Patients and methods: Patients undergoing 48-h ABPM within the National ABPM Registry of the Spanish Society of Hypertension, based on 800 Spacelabs 90207 monitors distributed throughout Spain in hypertension units and primary healthcare centres, were included. Between June 2004 and September 2005, 611 valid 48-h ABPM recordings were obtained, 235 corresponded to patients without antihypertensive treatment.
Results: The percentages of patients classified as non-dipper for the first 24 h, the second 24 h and the 48-h average were 47, 50 and 48%, respectively. When the first and second 24-h periods were compared, 147 (24%) subjects switched from dipper (D) to non-dipper (ND) or vice-versa. When the first 24-h period was compared to the 48-h average, 66 (11%) subjects switched patterns. The proportions were similar separately for systolic blood pressure (SBP) and diastolic blood pressure (DBP) and between treated and untreated patients. In subjects with poor ABPM reproducibility, night-to-day ratios were of an intermediate value between those of subjects always classified as D or ND.
Conclusion: Categorization of D or ND based on a single 24-h ABPM is moderately reproducible, since one out of every five patients change profile over the following 24 h. Nevertheless, the use of 48-h ABPM in clinical practice should be assessed according to cost-effectiveness criteria. Night-to-day ratios may be helpful in identifying patients with a stable profile.