Hypertension Control in Ambulatory Care Patients With Diabetes
Published Online: January 19, 2012
Rhonda BeLue, PhD; Adetokunbo N. Oluwole, PhD; Arnold N. F. Degboe, MB, ChB, PhD; and M. Kathleen Figaro, MD, MS
Type 2 diabetes mellitus (DM) is a major cause of morbidity and death, primarily through its microvascular and macrovascular complications.1-4 The macrovascular complications are related to blood pressure (BP) and blood glucose control and include myocardial infarction (MI), lower extremity amputation, and stroke.2-4 While new data caution against excessive BP and glucose control in certain subpopulations,5-7 studies continue to suggest that appropriate lowering of BP in diabetes is important for improving macrovascular outcomes.4-7
Hypertension (HTN) is common among patients with diabetes. The prevalence ranges from 60% to 80% of patients, depending on the sample and the patient’s race.8 The goal BP for those with type 2 DM is 130/80 mm Hg.8-10 Patients with diabetes whose systolic BP is 130 to 140 mm Hg are 46% less likely than those with uncontrolled systolic BP of over 140 mm Hg to die from any cause or suffer a nonfatal MI or stroke.4,6 The efficacy of HTN treatment for improving outcomes in type 2 DM is well documented by large trials showing benefits using both medications and lifestyle modifications.7,11 However, although HTN control among those with DM has improved over time, it is still less than ideal.12
Several clinical factors relate to unsatisfactory BP management of DM in the primary care setting, such as patient resistance to antihypertensive therapy, insufficient number of BP medications, side effects of medications, and provider clinical inertia. Racial and ethnic minorities, including blacks, Hispanics, and some Asian ethnic groups, are disproportionately affected by DM and are at increased risk for macrovascular complications.13-16 For example, black and Hispanic patients have a higher risk of stroke compared with white patients and benefit to the same extent as whites from use of medications to treat HTN.15-17
The goal of this study was to investigate HTN control among patients with diabetes in ambulatory care settings and to examine care setting characteristics, clinical variables, race, and sociodemographic status as they relate to HTN control among a national sample of patients with DM receiving care in diverse ambulatory care settings.
We hypothesized that patients with greater access to care as defined by treatment in private care settings would have a greater probability of achieving controlled BP. We also hypothesized that those who received not only medication but also weight management counseling would have a greater probability of having controlled BP. Lastly, we hypothesized that a minority of patients would have BP controlled to the American Diabetes Association (ADA) recommended level of 130/80 mm Hg and that underserved minority patients would be less likely to have that level of control compared with white patients.
This analysis uses extant data from the 2008 National Ambulatory Medical Care Survey and the National Hospital Ambulatory Medical Care survey (NAMCS/NHAMCS). The sampling framework is designed to obtain objective information about ambulatory medical care services in the United States. NAMCS data are collected based on a sample of visits to non-federally employed, office-based physicians who are primarily engaged in direct patient care. The NHAMCS consists of data on the utilization and provision of ambulatory care services in hospital emergency and outpatient departments. This study only includes ambulatory care outpatient visits from the NHAMCS database.
Patient Sample: All patients in the sample were diagnosed with type 2 DM and HTN and were 30 years of age or older. Patients with DM were identified via International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM) code (as indicated by the NAMCS/NHAMCS diagnosis variable) and/or by provider report on the patient intake form. Visits for diabetes were subset using the following: DM indicated as reason for visit, use of anti-diabetic agents, ICD-9-CM codes indicating DM, and provider indicating “yes” for a direct question asking whether patient has DM. The above approach minimized lost cases of DM. A total of 1313 patients with DM aged 30 years or older, with race/ethnicity categorized as white, black, Hispanic, or Asian, had a physician diagnosis or an ICD-9-CM code for HTN. Hypertension was identified using either reason for visit (HTN), use of anti-hypertensive drugs, ICD-9-CM codes indicating HTN, or direct indication of HTN as “yes” by provider.
Outcome of Interest: The ADA-recommended BP control goal of less than 130/80 mm Hg was used.8 Additionally, we assessed minimal BP standards at 140/90 mm Hg per treatment goals of the Seventh Joint National Committee (JNC 7) for patients without comorbidities, such as diabetes or chronic kidney disease. However, for patients with these comorbidities, the goal BP of <130/80 mm Hg is also recommended by JNC 7.9 Hypertension control was categorized into “controlled” or “uncontrolled.” The controlled group had systolic BP <130 mm Hg and diastolic BP<80 mm Hg during the index visit. The uncontrolled group consisted of patients with DM with 1 or more of the following: systolic BP >130 mm Hg or diastolic BP >80 mm Hg.8 We also assessed minimal control at BP >140 mm Hg or diastolic BP >90 mm Hg.
Demographics: Patient demographic characteristics included patient age in years, gender, income (above and below the median income), and insurance status (private, Medicare, or other; other included no charge/charity, Medicaid, self-pay, unknown.
Ambulatory Care: Variables related to the ambulatory care setting and visit included receipt of weight management counseling (yes or no); provider care setting was categorized into 3 setting types including free-standing physician offices, hospital outpatient departments and community health centers, and finally academic medical centers and other hospital settings.
Comorbidity: We evaluated for the presence of hyperlipidemia (yes/no) and body mass index (BMI) as indicated on the NAMCS/NHAMCS patient intake form. Obesity was defined as BMI of 30 or higher.
Anti-Hypertensive Drugs: Patients were categorized as using anti-hypertensive drugs (yes versus no). Anti-hypertensive drugs were identified based on level 2 categories in Multum Lexicon Plus. The categories were 1) angiotensinconverting enzyme inhibitors, angiotensin II inhibitors, renin inhibitors, anti-adrenergic agents (peripheral and central acting), beta-adrenergic blocking agents, calcium channel blocking agents, diuretics, vasodilators, aldosterone receptor antagonists, and 2) anti-hypertensive combination drugs. Additionally, the number of anti-hypertensive drugs was also calculated.
Analysis of variance and x2 tests were employed to examine the relationship between racial/ethnic group and HTN control, care setting characteristics, and patient characteristics. Binary logistic regression analyses were used to examine the relationship among outcome, HTN control, and candidate covariates, including race, income, provider, and facility characteristics controlling for patient demographic and health-status indicators. Regression analyses were run using Stata complex survey design procedures in order to obtain proper and robust standard errors. Variables not significant at P = .10 in bivariate regression were not entered into the final multivariable logistic regression model. Predicted probabilities were calculated using the Stata margins command. The predicted probability for the average marginal effect of each covariable on HTN control was estimated for each level of each covariable holding all other variables in the model at their means. P values reflect the statistical significance between each covariable and the probability of HTN control. Delta method standard errors were used to calculate confidence intervals. Confidence intervals indicate the precision of the predicted probability estimate.
Given the known disparities in HTN control by race and ethnicity, analyses are presented for the overall sample and by race and ethnic group.
Overall, approximately 28.7% of patients achieved HTN control at the level of 130/80 mm Hg and 57.0% at 140/90 mm Hg. On average, patients in this study were obese with a BMI of 32.7. The average age was 65.3 years and 53% were female. About 38% of patients had private insurance while 50.6% had Medicare, and 10.9% had other forms of insurance or were self-pay; 72.7% of patients were cared for in private physician offices and 13.6% were in outpatient departments or community healthcare centers, and 13.7% were cared for in academic medical centers or hospital settings (Table 1).
Patients seen in academic medical centers or other hospital settings had the greatest probability of HTN control (47.9% at 130/80 mm Hg and 70% at 140/90 mm Hg) compared with other outpatient settings. Patients with Medicare and private insurance had better control at both the 130/80 mm Hg and the 140/90 mm Hg levels, compared with patients on Medicaid, self-pay, or charity. In fact, Medicare patients had twice the probability of control compared with Medicaid, self-pay, or charity patients.
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