There is no widely accepted definition of white-coat or masked effects. Patients were therefore defined as displaying normal blood pressure characteristics, white-coat or masked effects objectively using statistically rigorous yet necessarily arbitrary thresholds. The sensitivity analyses conducted here demonstrate that altering these thresholds did not materially affect the predictive abilities of clinic blood pressure characteristics. Approximately, 42% of patients were observed to display a white-coat effect and 15% a masked effect. These proportions are similar to the previously reported estimations of the prevalence of white-coat (36–47%) [27,28] and masked hypertension (9–21%) [16,28–30] in treated patients with the caveat that such proportions vary depending on the population studied, how blood pressure is measured and how each condition is defined [31,32].
Other groups have compared multiple clinic blood pressure measurements with out-of-clinic blood pressure monitoring, but the current study is novel in its consideration of the drop, the slope and the shape of the change in blood pressure with repeated measurement. Previous work has shown that clinic blood pressure measurements taken with the BpTRU device are comparable with ambulatory blood pressure measurements in treated hypertensive patients [12,13,15]. In one study, Godwin et al.  showed that, in a treated and poorly controlled population, the mean of multiple clinic blood pressures predicts true controlled SBP (on the basis of ambulatory blood pressure monitoring) with a PPV of 80–87% and NPV of 49–59% (depending on the threshold used). However, this population had better blood pressure control than in the present study with many more results above and below the threshold for hypertension and so is not directly comparable. Further work should compare the two approaches in an untreated population being considered for diagnosis of hypertension and assess whether they are complementary.
The study is the first to consider how more detailed phenotyping of clinic blood pressure (measured using a simple method routinely available in clinical practice) might be used to reduce the need for additional more complicated blood pressure investigations such as ambulatory blood pressure monitoring. The ‘clinic blood pressure drop’ or the more complex algorithm based on slope and curve of multiple readings could be incorporated into a triaging tool for more targeted use of out-of-office blood pressure monitoring (see, for example, Boxes 1 and Boxes 2). This could be utilized (as it has been here) in treated hypertensive patients to optimize management. Future research should consider whether the same algorithm could be applied to an untreated or controlled group in order to assess the need for ambulatory blood pressure monitoring. The current diagnostic algorithm recommended in the UK guidelines  suggests that all patients with raised clinic blood pressure should be referred for out-of-office monitoring, whilst the European Society of Hypertension recommends out-of-office monitoring when white-coat or masked hypertension is ‘suspected’, although it is not clear how one would suspect them . Whilst the UK guidelines should improve the targeting of treatment to those without a white-coat effect, there is currently no reliable method to identify the masked effect [3,15]. Multiple clinic readings might fill this gap, although with the caveat that they may not identify all features from ambulatory monitoring such as nocturnal hypertension.
More work is needed to establish the appropriate thresholds for white-coat and masked hypertension using this new method in untreated patients with raised clinic pressure, those with normotension and those with apparently controlled clinic blood pressure. Further research could include evaluating the predictive abilities of multiple clinic readings for white-coat and masked effects when less than six readings are taken; whether the methodology requires a specific device (the BpTRU); and whether referring patients for out-of-office blood pressure monitoring on the basis of clinic blood pressure characteristics results in more or less unnecessary referrals than those approaches detailed in the new UK guidelines  and algorithms .
In conclusion, these data suggest, for the first time, that the characteristics of SBP measured repeatedly in a single clinic visit are predictive of clinical differences in blood pressure between repeated home and clinic measurements.
The authors would like to thank the patients and practices that took part in the original TASMINH2 study without whom this work would not have been possible.
Contributors: J.S., R.H., F.D.R.H. and R.J.Mc.M. had the original idea. J.S. undertook the analyses and wrote the first draft with R.J.Mc.M. and R.H. All authors subsequently refined the manuscript and approved the final version. R.J.Mc.M. is the guarantor.
Sources of funding: This study presents independent research commissioned by the National Institute for Health Research (NIHR) under its Programme Grants for Applied Research funding scheme (RP-PG-1209–10051). R.J.Mc.M. holds an NIHR Professorship. J.S. was funded by the NIHR Birmingham and Black Country Collaboration for Leadership in Applied Health Research and Care during part of this work, but now holds a Medical Research Council Strategic Skills Postdoctoral Fellowship. B.W. is a NIHR Senior Investigator and is supported by the NIHR UCL Hospitals Biomedical Research Centre. The TASMINH2 trial was funded by the UK Department of Health Policy Research Programme and the National Coordinating Centre for Research Capacity Development. The views and opinions expressed are those of the authors and do not necessarily reflect those of the NHS, NIHR, or the Department of Health. All equipment used in the study was purchased commercially.
The authors declare that they have no conflicts of interest.
Reviewer's Summary Evaluation Reviewer 1
Analysis of multiple clinic pressures device is compared with home blood pressure monitoring to arrive at predictors for deciding whether home monitoring will be helpful. Participants were part of the TASMINH2 trial and already on treatment. The question is whether six clinic pressures can accurately predict either the White Coat Effect or Masked Hypertension, so that home monitoring can be restricted to a targeted population. Clearly, additional studies of this issue are needed, but this report has important implications for management (i.e. home monitoring, yes or no) and especially for environments where home monitoring is impractical, yet the estimating White Coat effect or Masked Hypertension effect is needed.
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