The importance of home blood pressure (BP) monitoring amongst the various methods of determining a patient's hypertension status has increased dramatically in recent years with the development of low-cost, accurate and user-friendly devices. There has been a growing dissatisfaction with the accuracy of clinic measurements often determined in less than optimal conditions and contributing to a significant proportion of misdiagnosis due to the surprisingly high prevalence of white-coat hypertension and masked hypertension in particular . There have been a number of approaches to improve the accuracy of diagnosis with the wider use of ambulatory BP monitoring (ABPM) and the recognition that this technique is the gold standard when it comes to determining the patient's true BP status. Although there is convincing evidence from studies such as Hodgkinson et al. that ABPM is superior to clinic or home methods of measurement for diagnosis of hypertension, there is disagreement about whether ABPM could ‘replace’ clinic BP for this purpose [3,4].
There are a number of advantages of ABPM that include the large number of readings, which gives a very accurate picture of the patient's level of BP, providing the most comprehensive information for the diagnosis of hypertension and also with regard to optimizing the effectiveness of antihypertensive therapy. The technique is applicable in a wide range of patients including children, young adults, the elderly and also patients who are pregnant, obese or even those with intermittent cardiac arrhythmias. ABPM is also better than other techniques for diagnosing the presence of masked hypertension or white coat hypertension. Perhaps the most convincing argument for the wider use of ABPM particularly instead of clinic measurements of BP relates to its superior prognostic value. Although this may very well be due to the large number of BP assessments that would enable a more accurate measure of the patient's BP, a most notable aspect is the measurement during the night, which indicates the degree of BP dipping that can occur during sleep. There are a multitude of studies that have found that ABPM is a very strong predictor of clinical outcomes including end organ damage associated with high BP such as left ventricular hypertrophy and renal and vascular markers including microalbuminuria and carotid artery intima-media ratio [5–8]. Indeed, the strongest predictor of outcomes appears to be the nocturnal hypertension and/or nondipping [9–12]. The arguments in favour of using ABPM have been considered so strong that in 2011 in the United Kingdom, the National Institute for Health and Clinical Excellence guideline for the clinical management of primary hypertension in adults suggested that all new cases of suspected hypertension be confirmed with an ABPM where appropriate . Although advancing technology including easier to use devices and analysis software has made ABPM more attractive, there are some limitations in the high cost of the device as well as the cost of training staff to properly inform patients for its use . To counter this, a number of studies that have analysed the cost–benefit of ABPM have routinely shown that this technique overall reduces costs and saves healthcare budgets [15–17]. A study in 2011 showed that the reduction in misdiagnosis and reduced costs of therapy more than made up for the additional costs of the ambulatory service . A more recent study suggested that using ABPM to appropriately time the administration of antihypertensive therapy could produce additional savings by providing better control of BP both during the day and night . Thus, although the advantages and cost–benefits have been well demonstrated, the resistance to using ambulatory BP services remains a significant barrier to its use.
The use of home BP devices has increasingly become popular principally due to their convenience and low cost compared with an ABPM device. At present, home and self-measurement of BP is considered as an adjunct to clinic and ABPM rather than an alternative . There are now a number of guidelines that describe the appropriate use of home BP measurement and in general suggest morning and afternoon triplicate measurements each day for at least a week [20–22]. A systematic programme of self-assessment will provide a large number of readings over a period of weeks and possibly months depending on the enthusiasm of the patient. Indeed, home measurement is an important way of engaging patients in their own health care, and comparisons with clinic BP assessments show that home measurements are superior for predicting cardiovascular events and target organ damage [13,23–29]. Home BP measurements can be successfully used to detect white-coat and masked hypertension [30,31] and in larger studies have been shown to provide better hypertension management . However, there may well be considerable variation in the quality of recordings depending on the degree of training the patient has received and the phenomenon of the self-test effect that is somewhat similar to the white-coat effect observed in the office. Cuff size is of particular importance as too small a cuff will produce higher readings and lead to an underestimate of the degree of white-coat hypertension and overestimate levels of mask hypertension, particularly in patients with large arms . Thus, it is perhaps not so surprising that a direct comparison between home, office and ABPM in predicting outcomes showed that ABPM was prognostically superior to the other methods .
One of the major differences between standard ABPM and home measurements is the ability of the former to measure nocturnal dipping and hypertension that are known to be superior measures for predicting outcomes. A major breakthrough in this area has been the development of a home device that can be programmed to take several measures of BP during sleep. The HEM-5041 device from Omron (Omron Healthcare Co., Ltd., Kyoto Japan) was shown in 2009 to provide estimates of nocturnal BP in normal patients which were similar to those measured using ABPM . Interestingly, daytime measurements with the home device were lower than ABPM . A further technical advance has been the development of the Microlife WatchBP Home version N (Microlife, Widnau, Switzerland) that can also be programmed to measure nocturnal BP three times, which is suggested to be less disturbing but not as good as ABPM. Although these two devices are much cheaper than ABPM devices, they can almost be considered as more affordable hybrid devices. Indeed, if one programmed an ABPM device to only measure three times during the night, then there is very little difference except that during the day the ABPM device follows the patient during normal daily life activities, whereas the home measurements do not. This may explain the lower values with home measurement than with ABPM.
The critical question now is whether the additional BP measurements during sleep add to the prognostic value of home measurements. The focus of this editorial is therefore the manuscript by Kollias et al. published in this issue of the Journal of Hypertension, which is a systematic review and meta-analysis of the comparison of the association between night-time BP measured with a home device or during an ambulatory BP with target organ damage. The article is entitled ‘Association of night-time home blood pressure with night-time ambulatory blood pressure and target-organ damage: a systematic review and meta-analysis’. This is indeed a very timely review of the current state of the prognostic value of BP assessments as it has become very clear that the ability of home devices to measure nocturnal BP is a major step forward and possibly a ‘game changer’ given the resistance to the use of ABPM that has remained despite their clear status as the gold standard. Kollias et al. compares six studies of which three use the Omron HEM–5041 and three use the Microlife WatchBP version N. Interestingly, there doesn’t appear to be very much difference between these two devices in terms of the measurements compared with ambulatory recordings. Furthermore, the number of readings measured in each of the studies by either technique does not appear to play a major role. The main findings were that both the night-time home BP devices equally predicted measures of target organ damage with the one exception (urinary albumin excretion) in which the home BP device was better than the ambulatory device. One must also consider that there are limited studies included and that most (64%) of the patients came from one group. Also, there is a subtle difference between the home measurements and ABPM in that the former in some cases involved a variety of study durations. Approximately 30% of the patients were studied for two to three nights, whereas 10% studied for 1 week and 60% studied for as many nights as possible over 2 weeks. Thus, the information embedded in the data will include longer term variability and a different assessment of the nocturnal level of BP that is provided for by a one-off ABPM. This may well be a considerable advantage of the technique and one that has never been possible with ABPM. More than one or two nights’ assessments using ABPM would be considered as being far too onerous for the patient. Thus, the extra reading available at night during 2 weeks may be providing different information. The authors being well aware of this showed that the higher number of home device night readings correlated less well with nocturnal ABPM. The conclusion that the nocturnal measurement by a home or ambulatory device presents similar values and comparable relationships with target organ damage is an important finding and well based on the evidence presented in the study. This meta-analysis by Kollias et al. will provide a major stimulus in hypertension research for the development and wider use of nocturnal home devices. Clearly, there is a limitation on the use of ABPM for a variety of reasons, and there is an impetus for the development of validated quality home measuring devices, such as those from Omron and Microlife, which can include nocturnal measurements.
Conflicts of interest
There are no conflicts of interest.
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