The optimal schedule for self-home blood pressure monitoring

Abstract

In 2008, the European Society of Hypertension (ESH) [1] and the American Heart Association [2] published guidelines for self-monitoring of blood pressure by patients at home (HBPM), providing almost identical recommendations with only minor differences. Both guidelines recommended HBPM for long-term monitoring of treated hypertension and also for the initial diagnostic phase of subjects with elevated blood pressure (BP) [1,2]. Moreover, a common recommendation was given for the optimal HBPM schedule, which should be based on a 7-day monitoring with duplicate morning and evening measurements, and the average should be calculated after discarding readings of the first day [1,2]. The amount of research work, discussions and debate on the optimal HBPM schedule is a typical example of ‘knowing more and more for less and less’, as Tom Pickering stated in the foreword of his book on ‘Ambulatory Monitoring and Blood Pressure Variability’ [3]. Several studies investigated the performance of HBPM in the diagnosis of hypertension phenotypes (sustained, white-coat, masked hypertension) in untreated and treated subjects, by taking ambulatory BP monitoring (ABPM) as reference method and implementing different HBPM schedules (Table 1) [4–18]. Given that hypertension remains the leading risk factor for death and disability globally [19] and HBPM is recommended for almost all subjects with elevated BP [1,2], the optimal HBPM schedule indeed is highly relevant for cardiovascular disease prevention.TABLE 1: Diagnostic performance of home blood pressure monitoring versus ambulatory blood pressure taken as reference (studies in untreated subjects)In this issue of the journal, Nunan et al.[18] present the results of a carefully conducted study in 203 untreated subjects investigating the optimal HBPM schedule by taking ABPM as reference. The main conclusion of the authors is that 5-day HBPM provides the optimal schedule, and there is no additional benefit by performing more measurements or by excluding the first day. Strengths of this study are: (i) it was conducted in primary care where the vast majority of hypertensive patients are managed, (ii) validated HBPM devices and a tele-monitoring system were used, preventing thereby the ‘Achilles heel’ of the method, which is the misreporting of HBPM values by patients [20], and (iii) the HBPM schedule recommended by current guidelines was the basis of investigation [1,2]. However, (i) these results are limited to untreated subjects; (ii) diagnostic disagreement of HBPM with ABPM does not necessarily imply that the former is problematic; and (iii) systolic daytime ABPM differed by 7.5 mmHg from systolic HBPM [18], which contrasts with previous reports [1,2] and might have affected the study results. A critical overview of the evidence on the optimal HBPM schedule should address three main research questions: (i) Which is the minimum number of HBPM readings required for a reliable evaluation? (ii) Should readings of the first HBPM day be discarded? (iii) What are the pitfalls of taking ABPM as reference? MINIMUM NUMBER OF HOME BLOOD PRESSURE READINGS It is well established knowledge that with any BP measurement method (office, home, or ambulatory) by increasing the number of readings: (i) the average value is reduced, (ii) the variability [standard variation (SD)] is reduced, (iii) the reproducibility is improved, and (iv) the prognostic ability improved [21–24]. Indeed, it has been shown that the first HBPM reading gives the highest value, the most unstable one (highest SD) and with the weakest prognostic ability [21,23,25]. Furthermore, the first HBPM day gives higher average value than the next days, with higher SD and weaker correlation with ABPM [21]. It is therefore clear that a single HBPM reading or day does not exhaust the potential of the method, and more readings should be obtained. On the other hand, it is reasonable to expect that after obtaining a certain amount of HBPM readings, additional readings will not provide additional benefit. Brook [26] reviewed 12 studies using different HBPM schedules and concluded that variation in schedule has little impact on improving the relationship with ABPM and the majority of the benefits derived from the method are achieved by obtaining only a few measurements. Ohkubo et al.[23] analyzed data from the Ohasama outcome study and showed progressive increase in the prognostic value of HBPM by increasing the number of measurements within the range of 1–14 and concluded that preferably more than 14 measurements should be recommended for better prediction of stroke risk. Stergiou et al.[25] reported an analysis of the Didima outcome study and showed progressive increase in the prognostic value of HBPM by averaging more measurements within the investigated range of 1–12. Johansson et al.[27] showed that a minimum of 4-day HBPM is reliable in terms of association with ABPM and target organ damage. Other cross-sectional studies showed progress