Burden of Hypertension

One study estimated that the global prevalence of hypertension in 2000 was 26 percent in the adult population. It predicted a rise by 24 percent in developed countries and 80 percent in developing countries by 2025.⁴ The World Health Report 2002 estimates that over 1 billion people have hypertension, which is estimated to cause 4.5 percent of the global disease burden.⁵ In addition, high BP directly results in 7 million deaths annually.⁶ Within the United States, about 76.4 million adults are affected.⁷ Data from the National Health and Nutrition Examination Surveys (NHANES) from 1999 to 2008 indicated that 30 percent of all adults in the U.S. 18 years and older were hypertensive, with a higher prevalence among African Americans and the elderly.8 The prevalence of verified hypertension in children is more than 3 percent.² A study from 2002 reported a lifetime risk of developing hypertension among adults aged 55 to 65 years in the U.S. as greater than 90 percent.⁹ Despite improvements in the quality of health care and life expectancy, it is expected that the prevalence of hypertension will continue to rise as the population ages.

Hypertension is a major risk factor for cardiovascular disease and mortality and accounts for an estimated 14 percent of cardiovascular deaths worldwide and 18 percent in developed countries.¹⁰ It is an important modifiable risk factor for coronary artery disease, stroke, chronic kidney disease, congestive heart failure, and peripheral vascular disease.¹ The World Health Organization ranks high BP as the third highest risk factor for burden of disease, after underweight and unsafe sex, highlighting the contribution of hypertension directly and indirectly to the development of numerous diseases.⁵

Hypertension also imposes a heavy financial burden on society at large. The direct and indirect cost of high BP and its complications has been estimated at more than $43.5 billion in 2007 in the U.S.⁷ Thus, it cannot be viewed simply as an individual health issue given the large public health impact and the potential for cost savings with effective prevention or treatment.

Numerous health professional and government organizations have developed various guidelines for BP management. The choice of treatment is largely dependent on the cause of hypertension, severity of the condition, as well as the presence or absence of existing comorbid states. Recommended management strategies for BP control include lifestyle and behavior modification (such as smoking cessation, moderation of alcohol consumption, salt restriction and other dietary modifications, regular exercise, and weight loss in obese persons), usually combined with the use of antihypertensive medication. Effective BP control has been shown to decrease incidence for stroke by 35 to 40 percent, myocardial infarction by 20 to 25 percent, and heart failure more than 50 percent.^11,12 Systematic reviews have also shown the beneficial effects of lowering BP on reducing fatal and nonfatal stroke, cardiac events, and total among individuals with severe hypertension or at increased risk (such as of older age or with other comorbid risk factors).^11,13,14 A decrease of 5 mmHg in systolic BP has been estimated to result in a 14 percent overall reduction in mortality due to stroke, 9 percent reduction in mortality due to chronic heart disease and 7 percent reduction in all-cause mortality.^1,15,16 However, long-term adherence to lifestyle modification and medication remains a challenge in the management of hypertension, which is usually a lifelong condition.

BP Measurement Strategies

Strategies aimed at the control of high BP as well as adherence to medication continue to be of foremost concern to providers and patients, health care payers, policymakers, and governments worldwide. For appropriate diagnosis and therapy, accurate BP measurement is of great importance. However, consistently attaining reliable BP measurements is problematic. There is within-individual biological variability as well as measurement error. Repeated measurements are needed to facilitate accurate classification of patients. Other factors that can improve accuracy include the use of an appropriately sized cuff and slow cuff deflation. Measurements can be read by a person or provided digitally by a device. Readings by a person can be affected by observer training, preference, and bias. For example, terminal digit preference (i.e., preference for 0, 5, and even numbers) and single number preference (i.e., preference for specific values such as 130/80 or 140/90 mmHg) can lead to inaccuracies in measurement readings and variability across observers.^17,18 This can be prevented when machines provide readings automatically.

Current settings for BP measurement include BP measurement in a healthcare setting, or BP measurement in a patient's usual environment with either ambulatory BP monitoring, or self-measured BP (SMBP) monitoring. BP as recorded in the office or clinic setting at medical encounters is the most commonly used approach for measurement of BP. Reliable clinic measurements require an adequate rest period prior to measurement in order to enhance the consistency of BP readings. However, even when measured according to established guidelines, clinic BP measurements have several limitations. Clinic measurements may not reflect the usual BP outside of the clinic setting throughout a day. BP may rise in the clinic in response to the medical environment (referred to as white coat hypertension), or may be normal in the clinic but not outside of the clinic (referred to as masked hypertension).^19,20 Prevalence of white coat hypertension ranges from 10 to more than 20 percent,^21,22 and the prevalence of masked hypertension (MH) reaches 40 percent in some studies.²³ The prognostic significance of either is unclear.²⁴

There are two BP monitoring strategies that can currently be used at home: Ambulatory and SMBP monitoring. In brief, ambulatory BP monitoring is a noninvasive, fully automated technique in which BP is recorded over an extended period of time, typically 24 hours. A BP cuff is placed around the upper arm and left in place for approximately 24 hours. A connected monitor is preprogrammed to regularly record BP, usually every 15 to 20 minutes while awake and every 20 to 30 minutes while asleep. Patients are instructed to keep an activity log throughout the testing period for evaluation of stress- and activity-related BP changes. Ambulatory BP monitoring requires a technologist to program the machine, fit it on the patient, remove it and download the results and a physician to interpret them. Measurements may interfere with a patient's activity or sleep. Given the inconvenience and expense of setting up and using the device, ambulatory BP monitoring is predominantly used to diagnose white coat or masked hypertension, to identify people with abnormal daily BP patters, or to help with management of hard to control or highly variable BP. In addition, ambulatory BP monitoring is often used in research studies as an outcome, since many consider it to be more accurate than clinic-based BP measurement. It has been the subject of a 2002 Evidence Practice Center (EPC) Evidence Report.²⁵ A fuller description of ambulatory BP monitoring can be found there. The current report evaluates ambulatory BP monitoring only as an outcome measurement tool, not as an intervention of interest.

Self-measured BP (SMBP) monitoring is another option that allows for more frequent measurements, and possibly more accurate readings of a patient's typical BP.

Self-Measured Blood Pressure Monitoring

Technically, SMBP monitoring refers to regular measurement by the patient of his or her own BP. More broadly, though, it is the regular use of a BP measurement device that is owned by (or lent to) the patient to be used outside the office/clinic setting. The actual BP measurement can be done either by the patient, or less frequently by a companion, who is usually not a medical professional. SMBP measurements can be obtained from the upper arm, wrist, or fingers (or, if necessary, the lower extremity); however, experts recommend the use of upper arm devices due to the lack of validation and the high number of inaccurate measurements from the wrist and finger devices.^26-28 Models for SMBP devices range from mechanical aneroid gauges (sphygmomanometers), which require self-inflation and auscultation (“manual” devices), to manually-inflated sphygmomanometers with automatic displays (“semiautomated” devices), to fully automated configurations that automatically inflate the sphygmomanometer and measure the BP (“automated” devices). Many SMBP devices are commercially available. Many have undergone validation according to the recommendations of the American Association of Medical Instrumentation, the European Society of Hypertension or the British Hypertension Society.^25,29 Generally, the use of validated devices is preferred. Patients may require some instruction on how to use SMBP devices.^30,31

Generally, individuals with hypertension would use such devices at home to measure their own BP and provide written lists of readings to their provider at office visits. Newer SMBP devices can automatically store readings and some are equipped to electronically transmit readings to a provider. This may facilitate direct communication with a provider via phone call or email and result in shorter turn-around times in responding to a BP reading and thus ultimately to better BP control.

Proposed Advantages of Self-Measured Blood Pressure Monitoring

Self-measured blood pressure (SMBP) has been used in the treatment of hypertension with three major aims: 1) to avoid undertreatment of hypertension 2) to enhance self-participation in disease management and to enhance adherence; and 3) to avoid overtreatment in those with lower BP out of the clinic compared with in the clinic²⁶

SMBP is being used to avoid undertreatment of hypertension. SMBP monitoring can provide more frequent BP readings and if these are transmitted back to the provider, they can be used for more rapid and frequent adjustments in blood pressure medication to ensure adequate BP control. With training, additional support and treatment algorithms, patients may be able to self adjust medications based on SMBP results. However, there is uncertainty about the appropriate home BP targets for guiding treatment decisions and whether these should be based on the same cut-points from clinic BP or from ABPM for defining hypertension.³²

SMBP monitoring may be used as a tool for disease self-management and to improve adherence with lifestyle and diet modification, or with drug treatment. While patient self-participation in chronic disease management appears promising, the sustainability and clinical impact of SMBP remains uncertain. Finally, SMBP may be useful in preventing overtreatment in individuals with white coat syndrome, orthostatic BP changes, or hypotensive episodes from medication.

Whether or not to advise the use of an SMBP monitoring device for a patient with hypertension is a common clinical question for clinicians. The cost of a home BP monitor ranges between $40 to $150, and the insurance coverage and approval for these devices vary across states.³³ However, provision of the device could be cost-saving if it resulted in a reduced number of office visits for BP measurement or management or resulted in improved BP, which could translate into reduced morbidity and health care utilization. On the other hand, if more frequent home BP measurements lead to more encounters for counseling, modification of lifestyle behaviors, drug treatments along with management of adverse effects, SMBP may actually increase cost, at least in the short term, since it takes several years for improved BP control to improve clinical outcomes.

Current Uncertainties About Self Measured Blood Pressure Monitoring

There is no consensus on the precise protocol for SMBP monitoring in the management of hypertension regarding timing, frequency and duration. Neither is there consensus on how many serial measurements should be taken and which ones should be used or averaged to derive an accurate reading. SMBP monitoring may not be suitable in certain patients, such as those with arrhythmias and ectopic beats, large arm circumferences (as a too-small cuff size may give falsely elevated BP readings), with physical or mental disabilities that interfere with device operation. In addition, SMBP may carry the risk of unreliable BP readings if not obtained in a standard fashion, inappropriate self adjustments of antihypertensive medications, as well as increased anxiety in susceptible patients. As self-measurement requires patient participation, certain patient characteristics may affect compliance with SMBP monitoring, such as the willingness and ability to self-monitor BP and the technical literacy in operating the device or an interface for telemonitoring.

Further debate focuses on the role of additional support needed to enhance adherence with SMBP monitoring and, possibly, achieve the clinical benefit from it. For example it is unclear whether simply providing a device for SMBP will improve BP control or whether this needs to be combined with additional support such as the telemetric transmission of readings to a provider to allow more frequent titration of drugs, regular nursing contact, or other types of interactions with a provider regarding hypertension management. Figure 1 shows possible comparisons between SMBP, SMBP plus additional support, support without SMBP, and usual care. The bold lines indicate the comparisons addressed in the Key Questions (see below).

Figure 1

Possible comparisons between SMBP, SMBP plus additional support, support without SMBP, and usual care. SMBP = self-measured BP; KQ = Key Question The figure shows a schematic of possible comparisons between SMBP, SMBP plus additional, support without (more...)