Abstract and Introduction
Abstract
Study Objective: To examine the influence of specific patient characteristics on the success of ambulatory blood pressure monitoring (ABPM).
Design: Retrospective analysis.
Setting: University-affiliated family care center.
Patients: Five hundred thirty patients (mean age 52.7 yrs, range 14.90 yrs) who were undergoing ABPM between January 1, 2001, and July 1, 2007.
Measurement and Main Results: Specific patient characteristics were identified through an electronic medical record review and then examined for association with ABPM session success rate. These patient characteristics included age, sex, weight, height, body mass index (BMI), occupation, clinic blood pressure, travel distance to clinic, and presence of diabetes mellitus or renal disease. The percentage of valid readings obtained during an ABPM session was analyzed continuously (0.100%), whereas overall session success was analyzed dichotomously (0.79% or 80.100%). Univariate and multivariate regression analyses were performed to examine the influence of patient characteristics on the percentage of valid readings and the overall likelihood of achieving a successful session. In the 530 patients, the average percentage of valid readings was 90%, and a successful ABPM session (. 80% valid readings) was obtained in 84.7% (449 patients). A diagnosis of diabetes was found to negatively predict ABPM session success (continuous variable analysis, p=0.019; dichotomous variable analysis, odds ratio [OR] 0.45, 95% confidence interval [CI] 0.23.0.87, p=0.019), as did renal disease (continuous variable analysis, p=0.006; dichotomous variable analysis, OR 0.39, 95% CI 0.17.0.90, p=0.027) and increasing BMI (continuous variable analysis, p<0.001; dichotomous variable analysis, OR 0.78, 95% CI 0.65.0.93, p=0.005). Renal disease and BMI remained significant predictors in adjusted analyses.
Conclusion: For most patients, ABPM was successful; however, elevated BMI and renal disease were associated with less complete ABPM session results. Adaptation and individualization of the ABPM process may be necessary to improve results in these patients.
Introduction
The role of ambulatory blood pressure monitoring (ABPM) is well defined. It is recommended in several clinical situations, such as evaluation of “white coat' hypertension, treatment resistance, hypotension, episodic hypertension, and autonomic dysfunction. It has also proved helpful as a guide in the titration of antihypertensive therapy. Provision of ABPM to patients requires an organizational structure to complete several functions, including patient scheduling, patient education, cuff fitting and monitor setup, report analysis, and recommendation for treatment based on the information obtained from the session. Management of an ABPM service is a role well suited for clinical pharmacists involved in the management of hypertension. An ABPM referral service, codirected by a board-certified family physician and board-certified pharmacotherapist, has been in place at the University of Iowa Family Care Center (Iowa City, IA) since January 1, 2001. This pharmacist-physician collaboration has resulted in successful operation with approximately 600 referrals to the service since its inception.
Although most insurance carriers in the United States do not reimburse for the recommended ABPM indications, ABPM has been approved for reimbursement by the Centers for Medicare and Medicaid Services for patients with suspected white coat hypertension. Automated monitoring with use of ABPM offers several advantages over traditional office-based and home blood pressure monitoring, such as providing a more accurate estimate of a 24-hour blood pressure interval by eliminating observer bias and incorrect technique, allowing for examination of the diurnal blood pressure pattern, and stronger prognostic ability in predicting target organ damage.
There is potential for the use of ABPM to become even more widespread. However, with routine use of ABPM in all hypertensive patients, a substantial increase in health care costs could occur. It has been estimated that ABPM performed on 3–5 million patients would add $600 million to the cost of hypertension treatment. Other cost-effectiveness analyses have proposed that this estimate does not take into consideration the cost savings that ABPM may provide through prevention of unnecessary antihypertensive drug use and reduction in the number of follow-up visits required.
Not all patients with hypertension are candidates for ABPM, and not all candidates for ABPM are able to achieve a large number of valid readings during a 24-hour session. Thus, the potential cost savings afforded by ABPM depends on the ability to identify appropriate patients not only by indication, but also by the individual characteristics that will lead to a high success rate for the session. Although guidelines exist to help clinicians decide which indications may be appropriate for ABPM, we found no information describing specific patient characteristics that may influence the likelihood of achieving a high percentage of valid readings and, therefore, what would be considered a clinically useful ABPM session.
Since ABPM requires patients to wear a cuff and monitor for 24 hours, encompassing both awake and sleep times, problems may occur that lead to incomplete readings. Proposed standards for ABPM suggest that the number of valid blood pressure readings obtained during a session should be at least 80% of the total number attempted. Furthermore, this threshold is used in clinical trials in which patients are excluded if they obtained fewer than 80% of valid readings during an ABPM session. Clinical experience suggests that certain patient characteristics may lead to missed readings and, therefore, unsuccessful ABPM sessions. A priori identification of these patients may assist in controlling health care costs associated with ABPM, as more costeffective alternatives to ABPM may be used for these individuals. Alternatively, the current processes used for ABPM may be individualized to produce better results for these specific patients. The purpose of this study was to examine the influence of specific patient characteristics on the success of ABPM.