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AHRQ Evidence reports and summaries  AHRQ Evidence Reports, Numbers 61 - 11963. Utility of Blood Pressure Monitoring Outside of the Clinic Setting Evidence Report/Technology Assessment Number 63 Prepared for: Contract No. 290-97-006 Prepared by: AHRQ Publication No. 03-E004 November 2002 This document is in the public domain and may be used and reprinted without permission except those copyrighted materials noted for which further reproduction is prohibited without the specific permission of copyright holders. Suggested Citation:Appel L, Robinson K, Guallar E. Utility of Blood Pressure Monitoring Outside of the Clinic Setting. Evidence Report/Technology Assessment No. 63 (Prepared by the Johns Hopkins Evidence-based Practice Center under Contract No 290-97-006). AHRQ Publication No. 03-E004. Rockville, MD: Agency for Healthcare Research and Quality. November 2002. The Agency for Healthcare Research and Quality (AHRQ), through its Evidence-based Practice Centers (EPCs), sponsors the development of evidence reports and technology assessments to assist public- and private-sector organizations in their efforts to improve the quality of health care in the United States. The reports and assessments provide organizations with comprehensive, science-based information on common, costly medical conditions and new health care technologies. The EPCs systematically review the relevant scientific literature on topics assigned to them by AHRQ and conduct additional analyses when appropriate prior to developing their reports and assessments. To bring the broadest range of experts into the development of evidence reports and health technology assessments, AHRQ encourages the EPCs to form partnerships and enter into collaborations with other medical and research organizations. The EPCs work with these partner organizations to ensure that the evidence reports and technology assessments they produce will become building blocks for health care quality improvement projects throughout the Nation. The reports undergo peer review prior to their release. AHRQ expects that the EPC evidence reports and technology assessments will inform individual health plans, providers, and purchasers as well as the health care system as a whole by providing important information to help improve health care quality. We welcome written comments on this evidence report. They may be sent to: Director, Center for Practice and Technology Assessment, Agency for Healthcare Research and Quality, 6010 Executive Blvd., Suite 300, Rockville, MD 20852.
Objectives. Ambulatory BP (ABP) and self-measured BP (SMBP) monitoring are two techniques that record frequent BP outside of the clinic setting. The overall objective of this report was to summarize evidence on the clinical utility of ABP and SMBP monitoring. Electronic searches were completed of MEDLINE Articles were included in this evidence synthesis if they were English-language reports of original data that addressed one of the specific research questions in nonpregnant adults. Eighteen studies compared clinic BP, SMBP, and/or ABP. For both systolic and diastolic BP, clinic measurements exceeded SMBP and ABP. Few studies compared SMBP and ABP. Sixteen studies determined the prevalence of white coat hypertension (WCH). Overall, WCH prevalence was approximately 20 percent among hypertensives but varied considerably by definition. Few studies assessed the reproducibility of WCH (two studies) or the reproducibility of differences between clinic BP and either ABP (one study). In cross-sectional studies of BP with left ventricular mass and/or albuminuria (25 studies), ABP levels were directly associated with both measurements; also, left ventricular mass was less in individuals with WCH than in those with sustained hypertension. Ten prospective studies assessed the relationship of ABP with subsequent clinical outcomes. In each study, at least one dimension of ABP predicted outcomes. WCH predicted a reduced risk of CVD events compared to sustained hypertension. However, data were inadequate to compare the risk associated with WCH to the risk associated with normotension. A nondipping or inverse dipping pattern predicted an increased risk of clinical outcomes. The literature was insufficient to determine whether absolute SMBP levels or WCH based on SMBP was associated with left ventricular mass or proteinuria (just one study) or whether SMBP measurements predicted subsequent CVD (just one study). In both cross-sectional and prospective studies, the poor or uncertain quality of clinic measurements precluded a satisfactory comparison of SMBP and ABP with clinic BP. Twelve trials assessed whether use of SMBP had an impact on BP control. In half of these studies, including two trials that tested contemporary devices, use of SMBP was associated with reduced BP. The availability of just two ABP trials limited inferences about the utility of ABP to guide BP management. In general, few studies reported enrollment of African-Americans. Studies infrequently reported results stratified by gender. The only notable subgroup finding was a higher prevalence of WCH in women than men. In cross-sectional studies, ABP levels and ABP patterns were associated with BP-related target organ damage. Likewise, in prospective studies, higher ABP, sustained BP, and a nondipping ABP pattern were associated with an increased risk of subsequent CVD events. Few studies examined corresponding relationships for SMBP. An inadequate number of clinic BP measurements, as well as the poor or uncertain quality of these measurements, precluded satisfactory comparisons of risk prediction based on ABP or SMBP with risk prediction based on clinic BP. In aggregate, these findings provide some evidence that ABP monitoring is useful in evaluating prognosis. However, evidence was insufficient to determine whether the risks associated with WCH are sufficiently low to consider withholding drug therapy in this large subgroup of hypertensive patients. For SMBP, available evidence suggested that use of SMBP can improve BP control; however, further trials that evaluate contemporary SMBP devices are needed. Overview Elevated blood pressure (BP), also termed hypertension, is a common, powerful, and independent risk factor for cardiovascular diseases (CVD) and kidney disease. Approximately 25 percent of the adult U.S. population, about 50 million persons, has hypertension, defined as current use of anti-hypertensive medication, a systolic BP >140 mmHg, and/or diastolic BP > 90 mmHg. In view of the epidemic of high BP and its complications, prevention and control of high BP continues to be a major national health priority. Governments, institutions, health care providers, insurers, private industry, and non-profit organizations have committed substantial resources to prevent and treat hypertension. Still, hypertension control rates have been unsatisfactory. Measuring BP to diagnose hypertension and to monitor therapy is problematic. Concomitantly, the enormous scope of the BP problem, the high aggregate costs of hypertension care, and the potential for medication side effects have spawned efforts to target therapy more effectively. This entails identifying lower risk individuals who might be candidates for less aggressive therapy and higher risk individuals who should receive more aggressive therapy. Measurement of BP outside of the office or clinic setting by ambulatory BP (ABP) monitoring and self-measured BP (SMBP) monitoring might accomplish these objectives. BP as recorded in the office or clinic setting is the standard technique recommended for measurement of BP in routine medical care. The standard technique includes use of a mercury sphygmomanometer (or a calibrated aneroid device or validated electronic device) and an appropriate-sized cuff. Prior to measurement, patients should rest quietly in the seated position for several minutes. At each visit, at least two readings should be obtained. Except for those individuals with extremely high BP, the diagnosis of hypertension and adjustments in medication should then be based on the average of readings across two or more visits. Clinic BP measurements have several limitations, even if they are measured according to established guidelines. First, clinic BP measurements exhibit enormous variability, which hinders accurate classification and which frustrates providers and patients. Another limitation is that BP measured in the clinic may not be a representative estimate of usual BP outside the clinic setting. Commonly, BP rises in the clinic setting, in response to the observer and/or other aspects of the medical environment. The difference between measurements obtained in and outside the clinic setting leads to confusion about the diagnosis of hypertension and the need to start or modify therapy. Unfortunately, there are additional limitations because clinic measurements often do not conform to established guidelines. Specific limitations include lack of observer training, inadequate rest period prior to initial measurement, use of wrong-sized cuffs, rapid deflation of cuff, incorrect position of patients, and awkward position of the observer and/or manometer. Over the past several years, stationary automated devices and aneroid devices have increasingly replaced mercury sphygmomanometers in the clinic setting. Aneroid devices are inexpensive but still require an individual, typically a health care provider, to manually inflate a cuff and record the appearance and disappearance of Korotkoff sounds. In contrast, fully automated devices require minimal technical skills, that is, only placement of a cuff and initiation of a reading. An additional reason leading to greater use of aneroid and automated devices stems from concerns over mercury toxicity. SMBP devices include mercury sphygmomanometers, aneroid manometers, semiautomatic devices, and fully automatic electronic devices. Automatic devices measure BP using an oscillometric technique in which systolic and diastolic BP are estimated from the pattern of vibrations in the cuff as it is deflated. Fully automated devices are popular because the patient does not have to inflate the cuff or listen for the appearance and disappearance of Korotkoff sounds. Although numerous, perhaps hundreds, of SMBP devices are on the market, very few have been independently validated. SMBP devices provide an opportunity to record BP at home, outside of the artificial setting of the medical office or clinic. Ideally, the patient is trained to record BP using a standard technique. Occasionally, physicians may observe the patient recording a BP measurement in the clinic and then perform a cross check of readings. The presentation of SMBP data is extraordinarily variable. Commonly, patients at their own initiative provide written lists of readings to their physicians at office visits. However, recent innovations have greatly enhanced the potential utility of SMBP devices to synthesize and present data. Contemporary SMBP devices have the capacity to store and download readings via phone or computer. Data can then be synthesized and reports can be generated and sent to the patient and/or physician. SMBP has several potential uses. Repeated measurements, if averaged, should provide a more precise estimate of usual BP than occasional measurements obtained in the clinic. As a substitute for clinic BP, SMBP monitoring could then be used to adjust anti-hypertensive drug therapy and thereby reduce the need for frequent clinic visits and their associated costs and inconvenience. The extent to which physicians, or patients, use SMBP data to adjust medication is unclear. In addition, self-measurement of BP has also been proposed as a means to improve adherence with treatment. Self-measurement of BP theoretically provides a means to diagnose white coat hypertension (WCH), also termed non-sustained or office hypertension. This pattern refers to an elevation of clinic BP in the hypertensive range but normal or low BP outside the clinic setting. Individuals with WCH may be at comparatively low risk for BP-related complications in comparison to individuals with sustained hypertension. An important issue is whether the risk of WCH exceeds that of nonhypertensives. ABP monitoring is a noninvasive, fully automated technique in which BP is recorded over an extended period of time, typically 24 hours. The required equipment includes a cuff, a small monitor (attached to a belt), and a tube connecting the monitor to the cuff. Usually, a trained technician places the device on the patient, provides instructions to the patient, and then downloads data from the device when the patient returns. Most ABP devices use an oscillometric technique. Compared to SMBP, relatively few ABP devices are on the market. However, in contrast to SMBP devices, most currently available ABP devices have undergone validation testing, as recommended by the American Association of Medical Instrumentation (AAMI) or the British Hypertension Society (BHS). During a typical ABP monitoring session, BP is measured every 15 to 30 minutes over a 24-hour period (including both awake and asleep hours). The total number of readings usually varies between 50 and 100. BP data are stored in the monitor and then downloaded into device-specific computer software. The raw data can then be synthesized into a report that provides mean values by hour and period (daytime [awake], nighttime [asleep], and 24-hour BP), both for systolic and diastolic BP. The most common output used in decisionmaking are absolute levels of BP, that is, mean daytime, nighttime, and 24-hour values. Because of the expense of ABP equipment (up to $5,000 for a monitor, cuff set and software), the requirement for technicians, the inconvenience and logistics of placing and removing ABP devices, and, until recently, the lack of reimbursement, it is uncommon for ABP monitoring to be done frequently. However, use of ABP will likely increase as a result of the decision by the Centers for Medicare and Medicaid Services (CMS) to cover ABP in selected settings, namely, the identification of WCH. In addition to mean absolute levels of ABP, certain ABP patterns may predict BP-related complications. The patterns of greatest interest are white coat hypertension and nondipping BP. Using both daytime and nocturnal ABP, one can identify individuals, termed nondippers, who do not experience the decline in BP that occurs during sleep hours. Usually, nighttime (asleep) BP drops by 10 percent or more from daytime (awake) BP. Research has suggested that individuals with a nondipping pattern (less than 10-percent BP reduction from night to day) may be at increased risk of BP-related complications compared to those with a normal dipping pattern. Although ABP could be used to monitor therapy, the most common application is diagnostic, that is, to ascertain an individual's usual level of BP outside the clinic setting and thereby identify individuals with WCH. In addition to detection of WCH, ABP devices may be used to identify individuals with a nondipping BP pattern and to evaluate apparent drug resistance, hypotensive symptoms to medications, episodic hypertension, and autonomic dysfunction. Use of ABP monitoring has been controversial. First, few prospective studies have determined whether this technology predicts cardiovascular disease outcomes and whether this technology provides additional information beyond that of routine clinic measurements. Second, insurers have been concerned that health care providers might overutilize ABP. Third, it has been unclear whether SMBP monitoring is a satisfactory and less expensive alternative to ABP monitoring. Accordingly, health insurers have been reluctant to reimburse for ABP monitoring. The utility of BP monitoring outside of the clinic setting was a topic nominated to the Agency for Healthcare Research and Quality (AHRQ) by a group of experts in BP measurement. In September of 2000, AHRQ awarded a contract to the Johns Hopkins Evidence-based Practice Center (EPC) to prepare an evidence report on this topic. The Johns Hopkins EPC established a team and work plan to develop a report that would identify and synthesize the best available evidence on BP monitoring. One of the first tasks was the identification of an appropriate partner. In December 2000, the National High Blood Pressure Education Program (NHBPEP) of the National Heart, Lung, and Blood Institute (NHLBI) of the National Institutes of Health (NIH) hosted a working meeting. The NHBPEP includes representatives from national professional and voluntary organizations as well as from Federal agencies. Arising from that meeting was an agreement from the NHBPEP Coordinating Committee to partner with the Johns Hopkins EPC on this project. A core group of five clinically and/or methodologically oriented technical experts advised the EPC team at key points in the project. This group included experts in ABP monitoring, SMBP monitoring, clinic BP measurement, clinical hypertension, and diagnostic test evaluation. These individuals reviewed draft research questions. Also, this core group along with additional experts in BP measurement and hypertension provided early input at an ad hoc meeting convened by the NHBPEP. The target population consisted of nonpregnant adults with BP in the nonhypertensive or hypertensive range. These individuals are candidates for BP monitoring, and many are candidates for anti-hypertensive drug therapy. After an extensive deliberative process and with input from the technical experts, the following questions were developed:
 MethodologySearching the literature included identifying reference sources, formulating a search strategy for each source, and executing and documenting each search. A comprehensive search plan was developed that include electronic and hand searching. Several electronic databases were searched and a separate strategy was developed for each. First searched was MEDLINE Hand searching for possibly relevant citations took several forms. First, priority journals were identified through an analysis of the frequency of citations per journal in the database of search results as well as through discussions amongst the EPC team. Fifteen specialty and general journals were identified. The January to May 2001 issues of these journals were searched. For the second form of hand searching, a database of reference material, identified through an electronic search for relevant guidelines and reviews, through discussions with experts, and through the article review process, was created in the reference management software, ProCite. A listing of titles and abstracts from this database, the BP References Database, was reviewed by the principal investigator to identify key articles. The reference lists of these articles were then reviewed to identify possibly relevant citations. Finally, proceedings from recent conferences were also reviewed. Specific inclusion and exclusion criteria were applied at each of three levels of review (two levels of abstract review, then article review). Inclusion criteria became more stringent at each level. The titles and abstracts were reviewed for each article identified. During the abstract review process, emphasis was placed on identifying all articles that may possibly have original data pertinent to the questions. For the first-level abstract review, titles and abstracts for all articles retrieved by the literature search were printed on an abstract form and distributed to two reviewers. Because of the extensive volume of literature, a second level abstract review, at which additional exclusion criteria were applied, was necessary. Citations deemed eligible for full article review based on the initial abstract review were printed onto the second level abstract form and distributed to two reviewers. The purpose of the article review was to confirm the relevance of each article to the research questions, to determine methodological characteristics pertaining to study quality, and to collect evidence that addressed the research questions. Because of the large number of citations that remained eligible for full article review even after the second level abstract review, additional exclusion criteria were applied at the article review level. The final full list of exclusion criteria differed by question. For instance, for question 1a, a comparison of BP by the different techniques, the criterion of more than 1 day of measurement for clinic BP was added because an average clinic BP based on just 1 day of measurements (typically just one to three readings) is extremely imprecise and could lead to a biased comparison with ABP or SMBP. Article review forms were developed to collect data in a standardized fashion. This process was complex and time consuming due to the heterogeneity of the literature and the diverse questions being addressed. These forms then guided article review. For each of the articles deemed potentially eligible after second-level abstract review, two reviewers read the article, confirmed eligibility status, abstracted key information, and assessed study quality on several dimensions. Because of heterogeneity in study design, data collection forms and elements differed by research question. Evidence tables that summarize aspects of study quality, characteristics of the study population, and features of BP measurement were constructed. For most research questions, these summary tables were similar. However, the evidence tables that display study results differed substantially by research question. Qualitative summaries were prepared which synthesized the evidence and included, to a limited extent, a quantitative assessment (for example, the number/percent of studies with significant associations, and occasionally by relevant study characteristics). A draft version of the report was distributed to the partner, the technical advisory group, and other peer reviewers. All substantive comments were collated, the responses of the EPC team summarized, and edits were made to the report as appropriate.
In summary, ABP levels and ABP patterns were associated with BP-related target organ damage in cross-sectional studies. Likewise, in prospective studies, higher ABP, sustained hypertension, and a nondipping ABP pattern were associated with an increased risk of subsequent CVD events. Few studies examined corresponding relationships for SMBP. An inadequate number of clinic BP measurements, as well as the poor or uncertain quality of clinic BP measurements, precluded satisfactory comparisons of risk prediction based on ABP or SMBP with risk prediction based on clinic BP. In aggregate, these findings provide some support for use of ABP monitoring in evaluating prognosis. However, evidence was insufficient to determine whether the risks associated with WCH are sufficiently low to consider withholding drug therapy in this large subgroup of hypertensive patients. For SMBP, available evidence from several trials suggested that use of SMBP can improve BP control; however, further trials that evaluate contemporary SMBP devices are needed. The optimal approach to measure BP remains uncertain. In view of the high prevalence of uncontrolled hypertension, the continuing epidemic of BP-related diseases, and the potential for alternative measurement techniques to improve diagnosis and target therapy, there is a need for comparative studies that assess the relative efficacy, feasibility, and costs of ABP, contemporary SMBP technology, and clinic BP. Specific types of research needs are as follows:
In future research, clinic BP should be measured appropriately by trained observers using validated equipment; measurements should be obtained at several visits. Also, because of the dearth of large-scale, high-quality studies, there is a clear need for government sponsorship of key studies. To improve the quality of ABP and SMBP publications, standardized methods should be disseminated to researchers and authors. Also, journals should require standardized approaches for presenting ABP data. For published articles, full copies of protocols should be made available, perhaps on the Web. This is especially important because the intense pressure from editors to shorten manuscripts typically leads to reductions in the methods section. The full evidence report from which this summary was taken was prepared for the Agency for Healthcare Research and Quality (AHRQ) by the Johns Hopkins Evidence-based Practice Center (EPC), Baltimore, MD, under contract number 290-97-006. It is expected to be available in fall 2002. At that time, printed copies may be obtained free of charge from the AHRQ Publications Clearinghouse by calling 800-358-9295. Requesters should ask for Evidence Report/Technology Assessment No. 63, Utility of Blood Pressure Monitoring Outside of the Clinic Setting. In addition, Internet users will be able to access the report and this summary online through AHRQ's Web site at www.ahrq.gov. |
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, Cochrane Collaboration CENTRAL Register of Controlled Trials, and HealthSTAR. Hand searching was completed of key journals, conference proceedings and references lists. Electronic searching was completed to March 2001, and hand searching was completed to May 2001.