High blood pressure (BP) is the leading modifiable risk factor for cardiovascular disease, contributing to the greatest global burden of disease [1,2]. There are major deficiencies with respect to optimal awareness, diagnosis and treatment of high BP, and these problems persist across low-income, middle-income and high-income countries, altogether emphasizing the need for widespread population-level improvement . Reassuringly, if the presence of high BP can be correctly identified with appropriate use of accurate BP devices and BP measurement protocols, the risk of future cardiovascular events can be reduced significantly with BP-lowering medications , dietary and lifestyle interventions .
The accurate measurement of BP and the diagnosis of hypertension are crucial because misclassification can have serious clinical consequences . An overestimation of BP based on inaccurate measurement could lead to the initiation, and potential lifelong continuation, of unnecessary medications with possible side effects as well as unwanted social effects including anxiety, workplace absenteeism  and increased costs from insurance and medications . Conversely, if inaccurate measurement results in underestimating BP, an opportunity to prevent avoidable cardiovascular events may be missed. These are nontrivial problems, in that relatively small systematic inaccuracies can lead to misclassification of many millions of people at the population level . Thus, accurate BP measurement has been cited as one of the most important tests in clinical medicine . The accuracy of BP measurement is a serious and frequent problem of contemporary clinical practice that should be considered as an issue of patient safety.
One of the key actions of The Lancet Commission on Hypertension was to improve BP evaluation from better quality of BP measurements through endorsed protocols and validated (accurate) BP monitors . Manufacturers must adhere to strict regulatory processes to bring a BP device legally to market. However, many loopholes have been identified which lead to BP devices of poor or unknown accuracy being widely available for clinic use, including for self-monitoring at home [12–19]. The effects of unknown BP errors can influence the clinical environment, epidemiology and research, and even contribute to discrepancies among hypertension guidelines . From about 3000 cuff-based BP measuring devices on the market today, less than 15% have published evidence on accuracy performance . These nonvalidated BP devices are used in clinical practice and are more likely to be inaccurate [22–24]. Furthermore, a variety of new BP measurement technologies using sensors and cuffless techniques are also now emerging for sale, but there is minimal guidance on appropriate standards for accurately testing them.
The aim of this article is both to summarize the current situation regarding the regulatory requirements and accuracy standards for BP measuring devices, and also to redress the problems mentioned above by providing recommendations and actions towards improving validation and reporting standards for BP measuring devices. This article is fully aligned with the WHO policies on medical devices and can assist to catalyse the full implementation of the related World Health Assembly resolutions [25,26]. Ultimately, this work seeks to facilitate the global availability of validated BP measuring devices, thereby increasing the probability of better BP management and decreasing the worldwide burden of high BP.
HOW A BLOOD PRESSURE DEVICE BECOMES APPROVED FOR SALE
Many countries have legal processes in place, whereby a manufacturer of a BP device must demonstrate compliance with regulatory requirements before being given clearance for sale of the device. It is beyond this review to detail the specific regulatory processes among different countries, as these differ across the world and involve substantial complexity. However, the general overriding principles of regulatory processes are to ensure that BP devices meet acceptable standards of quality, safety, reliability and effectiveness (e.g. suitability for intended purpose).
If a company decides to market a BP device, it must submit an application that is reviewed by the regulatory authority within the jurisdiction of sale [e.g. the US Food and Drug Administration (FDA, USA); Therapeutic Products Directorate (Canada); or Therapeutic Goods Administration (Australia), to name a few]. If the information provided by the manufacturer meets the local regulatory requirements, a licence (or clearance) is issued for sale of the device within that country. In general, there are increasing levels of regulatory requirements and assessments as the level of potential risk from the device to the consumer rises. Thus, as BP devices are classified as low-to-moderate risk, the regulatory requirements are lower than those for high-risk medical devices.
Although not required by law, a common way for the manufacturer of a medical device to demonstrate compliance with regulatory requirements is to show that the device conforms with published standards relevant to that device. Standards are documents designed to set out the specifications, procedures and guidelines to ensure the quality, safety and effectiveness of devices. The International Organisation for Standardization (ISO) develops standards for use globally, but separate national or regional standards may also exist.
STANDARDS FOR ASSESSING THE ACCURACY OF BLOOD PRESSURE MEASURING DEVICES
Efforts to validate BP devices formally started in the 1980s . In 1987, the US Association for the advancement of medical instrumentation (AAMI) developed a clinical validation protocol for BP devices [28,29], which was followed by a similar protocol from the British Hypertension Society [30,31]. In 1999, the German Hypertension League developed another protocol  and in 2002 the European Society of Hypertension (ESH) Working Group on BP Monitoring developed their International Protocol, which they revised in 2010 [33,34]. These protocols have been revised by adopting more stringent criteria [29,31,34]. In 2004, the European Committee for Standardization (CEN) published another standard , and in 2009 the ISO also developed a standard  largely based on the AAMI and CEN standards. This was adopted by AAMI . In 2013, a revised version of the AAMI/ISO Standard was published .
While the abovementioned validation protocols and standards have similarities in concept and core procedures, they also have several methodological differences regarding important issues such as the sample size required, selection criteria for the participants, the validation procedure, the efficacy measure and the criteria to pass . This variation has confused researchers, physicians, consumers and manufacturers as to which protocol should be preferred and why. Furthermore, even when allegedly following recommended protocols, investigators can make incorrect claims about validation . After three decades of persistent efforts by several prestigious organizations for optimizing the validation process there is no doubt that science, the public, the regulatory bodies and industry would be best served if a single standard for validation of BP monitors is agreed and universally accepted.
In 2017, an international initiative to establish a universally acceptable standard for evaluating the accuracy of BP measuring devices was put in place by the AAMI, ESH and ISO committees . This Standard (ISO 81060-2:2018)  consolidates previous evidence and will progressively replace all previous protocols used around the world. In order for this initiative to achieve global impact for increasing the availability of BP devices validated for clinical accuracy, it would be necessary to make it mandatory to use the universally accepted ISO Standard for assessing the accuracy of BP measuring devices before they are put on the market for use in the medical, community and home settings.
REGULATORY PATHWAY PROBLEMS AND OUTCOMES FOR BLOOD PRESSURE DEVICES
There are significant problems in the transmission of scientific data on BP device accuracy to the actual users of such devices [15,16,41,43–45]. Many important articles on the deficiencies of BP measurement have been published over many decades [10,46], but the information is rarely disseminated beyond the researchers and health professionals who are already familiar with the problems. Manufacturers may be aware of the limitations with respect to BP device accuracy, but while the consumer market remains unaffected, there is little impetus to modify practice.
A fundamental regulatory problem is that authorities focus mainly on the physical safety features of BP devices rather than accuracy and performance characteristics [15,43]. Indeed, manufacturers are not required to test accuracy according to specific unified standards, nor to share results of the accuracy testing publicly. Regulations can also be difficult to enforce due to ambiguities and high levels of complexity . In addition, recommendations from consumer organizations are often based on cost, usability and cosmetics rather than accuracy. Most insidiously, unethical manufacturers are selling cheap home BP devices online and making false claims with respect to validation . This implies that consumers may be more likely to purchase lower priced, nonvalidated devices, but this needs to be confirmed. Many other problems, summarized in Table 1, have resulted in a marketplace replete with BP devices of unknown or questionable accuracy [21–24].
EMERGING NEW BLOOD PRESSURE DEVICE METHODS AND TECHNOLOGIES
Clinical guidelines for the diagnosis and management of hypertension have been developed based on evidence from auscultation or oscillometric arm cuff BP devices, which remain the recommended standard for clinical practice. These methods rely on analysis of haemodynamic signals in the brachial artery, which were originally believed to be a good estimate of the central aortic pressure load  as the most clinically relevant BP [49–53]. In reality, cuff BP devices vary greatly as to whether the measurements represent central aortic or even brachial BP, and there may be large individual variation in the SBP at the central aorta compared with the brachial artery (e.g. difference >30 mmHg) . There are a variety of devices available that purport to measure central aortic BP, as distinct from standard cuff BP . However, beyond recommendations of professional societies , there are no regulatory standards to assess performance of these devices.
There is also a burgeoning of new BP measurement technologies that seek to measure BP in entirely different ways than cuff BP. These include different types of cuffless sensors at various arterial sites (e.g. chest, face, upper arm, wrist, finger) with continuous or ‘snapshot’ monitoring of BP using a variety of direct or indirect recording and signal processing methods (e.g. reflectance pulse oximetry, radio frequency sensors, microstructure strain gauge fibres, opto-electronic, applanation tonometry, pulse transit time, smartphone applications) over durations that may extend to weeks or months, and may incorporate software programs with clinical decision-support functionality [57–66]. Some of these methods are not user-friendly and many still rely on calibration to a conventional cuff-based BP measurement, which are limiting features. Nonetheless, this is an evolving field with major opportunities to improve hypertension evaluation and control, and also to advance systems of healthcare delivery by merging with electronic medical records. However, these diverse technologies also pose new regulatory challenges in providing suitable oversight regarding clinical performance, accuracy, safety and utility .
RECOMMENDATIONS AND ACTIONS TO ADDRESS IDENTIFIED PROBLEMS
Recommendation 1: Convergence toward the global regulatory requirement for mandatory independent validation of BP devices according to the universally accepted ISO Standard (ISO 81060-2:2018) with publication preferably in a peer reviewed journal
According to the WHO, high-quality health technologies, such as validated BP devices, are indispensable for effective universal healthcare delivery . Indeed, the WHO Global Model Regulatory Framework for Medical Devices presents a stepwise approach to implementing and enforcing regulatory controls for medical devices . Regulatory convergence is when the regulatory requirements across different regions become aligned due to the adoption of internationally recognized technical documents or regulatory mechanisms that align with achieving a common public health goal . The ISO Standard fulfils the urgent need for a single, universally accepted protocol for BP device validation. The standard has already been adopted by the United States, as well as many other countries and, if made a global mandatory regulatory requirement, will redress the majority of problems relating to BP device accuracy associated with current frameworks. For this to occur there are numerous actions that need to be undertaken across a wide spectrum of key stakeholders that include: government organizations (e.g. FDA or other regulatory agencies); nongovernment organizations (e.g. hypertension societies); researchers, health professionals; journals that publish material related to BP; manufacturers of BP devices and the consumers who purchase BP devices. Nongovernment organizations have many important roles to play. Indeed, endorsement of a standardized validation protocol by a hypertension society has been shown to influence manufacturers to pursue independent validation of BP devices . A summary of required actions is detailed in Table 2.
Recommendation 2: Development of specific standards for the validation of new BP measuring technologies that cannot be tested using the ISO Standard (ISO 81060-2:2018)
The worldwide inundation of new technology that claims to measure BP brings challenges to regulatory authorities that are also encouraging ways to find innovative solutions . Rather than repeating past regulatory problems experienced with standard cuff BP devices, there is an opportunity for developing international standards that are specific to new BP technologies, and that appropriately evaluate accuracy and clinical validity. Table 2 sets out the actions required to achieve this recommendation. As with Recommendation 1, both government and nongovernment organizations will need to undertake actions to develop the specific standards and legislate for their mandatory use before approval for sale, but also endorse, regulate and monitor compliance with the new standards. Health professionals should avoid using new BP technologies to inform clinical management until the method in question can be proven to enhance clinical care.
Recommendation 3: Accredited online lists of BP devices detailing the published results of the validation studies
There is an urgent need to establish means of informing the scientific and general community as to which BP devices have been tested and found to have acceptable accuracy. This can be achieved through online lists of BP devices that detail the results of validation studies carried out according to international standards . The lists should be developed and maintained by organizations with sufficient expertise to ensure scientific rigor and remain independent from BP device manufacturers. Such lists have been developed by national scientific societies in the United Kingdom  and Canada . The American Medical Association and the American Heart Association , as well as an international group of BP measurement experts (STRIDE-BP organization) have also developed similar resources for general use, which are important nonprofit initiatives. As we move towards a single, universally-accepted ISO Standard, so too we should work towards developing one universally accepted accredited list of BP devices to consolidate information for best effect. Table 2 summarizes the actions and key stakeholders to achieve this recommendation.
IMPLEMENTATION ACTIONS BY THE LANCET COMMISSION ON HYPERTENSION GROUP
A co-ordinated program of activities to implement the recommendations and actions set out in Table 2 is being led by an executive team from the Lancet Commission on Hypertension Group. This team will be guided by an advisory team of invited members with relevant expertise across diverse skills (e.g. scientific, technical, advocacy, implementation science) and representing organizational sectors (e.g. government and nongovernment organizations, professional societies) in different world regions. Lobbying key decision-makers at national Department of Health level is recognized as critical for successful knowledge transfer. The executive team is also keen to leverage opportunity for implementation through existing international programmes and resources, such as the WHO Programme on Cardiovascular Disease, and among individual countries through local champions and relevant organizations (e.g. Heart and Stroke Foundations). The outcomes of these activities will be evaluated and published. Interested partners can contact the corresponding author of this article.
Measurement of BP is a fundamental medical test performed daily on many millions of people worldwide, and health professionals together with consumers should have confidence in the accuracy of the BP devices that they use for screening, diagnosis and management of hypertension. On the contrary, due to a host of well known problems, the global marketplace has been inundated with BP devices that are either known to be inaccurate or are of unknown accuracy. This can have serious implications for being able to achieve best-practice care of people related to BP control. The problem also threatens to be compounded by widespread introduction of new technology purporting to measure BP. Fortunately, most identified problems could be resolved by the mandatory requirement for independent validation of BP devices according to the recently developed ISO Standard. Other key needs are the development of specific standards for the validation of new BP technologies and accredited online lists of BP devices that are accessible to health professionals and consumers. An executive team of the Lancet Commission on Hypertension Group is currently working towards implementation of the recommendations provided in this position statement. Adherence to these recommendations would align with WHO policy to result in more accurate diagnosis and treatment of hypertension and a decrease in the worldwide burden from high BP.
The Lancet Commission on Hypertension Group members are Michael H. Olsen, Sonia Y. Angell, Samira Asma, Pierre Boutouyrie, Dylan Burger, Julio A. Chirinos, Albertino Damasceno, Christian Delles, Anne-Paule Gimenez-Roqueplo, Dagmara Hering, Patricio López-Jaramillo, Fernando Martinez, Vlado Perkovic, Ernst R. Rietzschel, Giuseppe Schillaci, Aletta E. Schutte, Angelo Scuteri, James E. Sharman, Kristian Wachtell, Ji-Guang Wang.
The following organisations and institutions endorse this position statement: Lancet Commission on Hypertension Group, American Heart Association, American Medical Association, Artery Society, Brazilian Society of Cardiology, British and Irish Hypertension Society, Chinese Hypertension League, Danish Heart Foundation, Danish Society of Hypertension, European Society of Hypertension Working Group on Blood Pressure Monitoring and Cardiovascular Variability, Finnish Hypertension Society, French Society of Hypertension, High Blood Pressure Research Council of Australia, Hypertension Canada, International Society of Vascular Health, Korean Society of Hypertension, Latin American Society of Hypertension, National Heart Foundation of Australia, Norwegian Society of Hypertension, Pan American Health Organisation, Resolve to Save Lives, Swedish Society of Hypertension, Stroke and Vascular Medicine, World Hypertension League.
No funding was received for this work.
Conflicts of interest
J.E.S.'s university has received equipment and research funding from manufacturers of BP devices including AtCor Medical, IEM and Pulsecor (Uscom). He has no personal commercial interests related to BP companies. E.O. conducted validation studies for various manufacturers of BP measuring technologies and advised manufacturers on device and software development. B.A. conducted validation studies for various manufacturers of BP measuring technologies and advised manufacturers on device and software development. A.E.S. has received equipment and funding from manufacturers of BP devices including IEM and Omron. C.D. and M.H.O. have no conflicts. R.A. conducted validation studies for various manufacturers of BP measuring technologies and advised manufacturers on device and software development. N.A. is the Chief Analytics Officer of Medaval Ltd., which provides validation information and listings to the public and validation and equivalence services to manufacturers; has conducted validation studies for various manufacturers of BP measuring technologies and has advised manufacturers on device and software development. E.B. and D.C. have no conflicts. N.R.C.C. was a paid consultant to the Novartis Foundation (2016–2017) to support their programme to improve hypertension control in low-to-middle income countries which includes travel support for site visits and a contract to develop a survey. He has provided paid consultative advice on accurate blood pressure assessment to Midway Corporation (2017) and is an unpaid member of World Action on Salt and Health (WASH). J.C. has received a research grant from Idorsia for the SPIRIT study of resistant hypertension. G.J. has no conflict. S.L. has received equipment and research funding from manufacturers of BP devices including AtCor Medical and Omron. P.B. has received honorarium and grants from Withings. P.L.-J. has no conflict. R.M. has received BP monitors for research from Omron. He chairs the British and Irish Hypertension Society's Working Group on Blood Pressure Measurement. A.M., P.O. and S.A. have no conflicts. R.P. is the Canadian representative to the ISO Sphygmomanometer committee and sits on the AAMI Sphygmomanometer committee. Co-Founder of a BP measurement start-up company (mmHg Inc.), based at the University of Alberta, with no products currently on the market. P.P. has received income from Hingmed (China), Novacor (France) and A&D (Japan). G.P. conducted validation studies for various manufacturers of BP measuring technologies and advised manufacturers on device and software development. N.P.: The International Society of Hypertension received BP devices from Omron to carry out a screening campaign when Dr Poulter was President of the Society. M.K.R. is the Vice President, Improving Health Outcomes at American Medical Association. C.R. has received digital BP monitors for research from Omron. F.S. conducted validation studies for various manufacturers of BP measuring technologies. A.S., W.S.B., M.-C.C. and K-CS have no conflicts. R.R.T.: Advisory Board Consultant for Hill_Rom. J.-G.W. conducted validation studies for various manufacturers of BP measuring technologies and advised manufacturers on device and software development. T.W.-H. has no conflicts. G.W.: Director, Outcomes Analytics at American Medical Association. G.S.: ISO Sphygmomanometer committee member; Chairman of European Society of Hypertension Working Group on BP Monitoring and envoy to the ISO Sphygmomanometer committee. Conducted validation studies for various manufacturers of BP measuring technologies and advised manufacturers on device and software development.
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