|Home | About | Journals | Submit | Contact Us | Français|
Expanding insurance coverage, while necessary, may not be sufficient to ensure high quality care for adults with cardiovascular disease. We sought to examine the association between having a usual source of care (USOC) and receiving medication treatment for hypertension and hypercholesterolemia.
Using the 2003-2006 National Health and Nutrition Examination Survey (NHANES), we categorized USOC (a place to go when sick or need medical advice) and insurance status in adults ≥35 years with an indication for medication treatment of hypertension (n=3,142) and hypercholesterolemia (n=1,134), determined using the Joint National Committee 7 and Adult Treatment Panel III recommendations, respectively. Multivariable logistic regression modeling was used to determine the independent effect of USOC on receiving treatment for hypertension and hypercholesterolemia, controlling for age, sex, race/ethnicity, insurance status, and comorbidities. Separate multivariable models were examined stratified by insurance status.
Among subjects with an indication for treatment of hypertension and hypercholesterolemia, 32.4% and 42.0% were untreated, respectively. When compared with adults with a USOC, adults without a USOC were more likely to be untreated for hypertension (adjusted prevalence ratio [aPR]=2.43, 95% Confidence Interval [CI]: 1.88-2.85) and hypercholesterolemia (aPR=1.79, 95%CI: 1.31-2.13). In stratified analyses among subjects with insurance, no USOC remained associated with being untreated (hypertension, aPR=2.58, 95%CI: 1.88-3.08; hypercholesterolemia, aPR=1.65, 95%CI: 0.97-2.18).
Absence of a USOC was associated with being untreated for hypertension and hypercholesterolemia, even among individuals with insurance, suggesting that efforts to improve chronic disease management should also facilitate access to a regular source of care.
Having a usual source of care (USOC), defined as a regular place to go when you are sick or in need of medical advice, has been associated with receiving higher quality preventive care.1-4 Adults with a USOC are more likely to receive recommended screening tests for hypercholesterolemia, hypertension, and cancer, along with vaccinations for influenza.1, 5-8 However, less is known about the impact of a USOC on appropriate chronic disease management. Two older studies found that a USOC was important for the treatment and control of hypertension, while more recent studies found the same when examining hypercholesterolemia and diabetes care.3, 9-12
Chronic illness affects over one-third of the U.S. population, and most adults do not receive appropriate or recommended care.13-14 Data suggest that the underuse of medication for cardiovascular disease (CVD) risk factors is in part due to poor access-to-care, specifically the lack of insurance coverage.15-23 However, not having a USOC, in addition to lacking insurance coverage, may additionally contribute to the underutilization of effective therapies.14, 24-25 If so, then new policies to increase insurance coverage must be coupled with efforts to expand the health system's capacity to provide a USOC.
To examine the relationship between a USOC and effective chronic disease management, we focused on the treatment of two common CVD risk factors among a nationally representative sample of the U.S. adult population. Specifically, we studied the independent association of having a USOC with receiving appropriate medication therapy for hypertension and hypercholesterolemia. We further examined the importance of having a USOC with respect to insurance coverage, stratifying the study groups by insurance status and testing the main effects of USOC on the primary outcome. We hypothesize that USOC will be important for receiving medication therapy, independent of insurance status. This distinction will help inform ongoing efforts to organize a healthcare infrastructure that can support high-quality chronic disease care.
Data come from the National Health and Nutrition Examination Survey (NHANES). Conducted by the National Center for Health Statistics, NHANES collects detailed health and nutritional data on a nationally representative, multistage probability sample of the non-institutionalized civilian population of the US. NHANES includes both an in-home interview and a clinical examination at a mobile examination center (MEC). A subsample of respondents, selected at random with a specified sampling fraction, provide a fasting blood sample as part of the MEC examination. This subsample has its own designated weight, which accounts for the additional probability of selection into the subsample component, as well as non-response. For this study, we combined data from two NHANES cohorts: 2003–2004 and 2005–2006.
Data analysis was restricted to men and women ≥35 years with an indication for treatment of either hypertension or hypercholesterolemia. For the hypertension group, subjects were eligible if they participated in the MEC (n=6,762). For the hypercholesterolemia group, subjects were eligible if randomized to the fasting blood draw sample (n=2,832).
In the hypertension group, indication for treatment was determined by self-report, review of the Lexicon Plus® medication file, and mean blood pressure readings. Persons with either no blood pressure measurements or three invalid measurements were excluded. Persons were considered “treated” if they responded ‘yes’ to the following questions: (1) ever told by a doctor or other health professional that you have high blood pressure; (2) because of high blood pressure, were you ever told to take a prescribed medication; and (3) are you now taking a prescribed medication, and were confirmed to be taking an antihypertensive medication (angiotensin converting enzyme (ACE) inhibitor, angiotensin II receptor blocker, diuretic, beta-adrenergic blocker, calcium channel blocker, vasodilator, centrally or peripherally acting antiadrenergic medication, or antihypertensive combination).26 It was necessary to include self-report of antihypertensive medication use, as persons may be taking one or more of the above classes of medication for an indication other than hypertension. Adults who reported taking an antihypertensive medication that was not confirmed in the medication file were considered “untreated.”
For persons who responded ‘no’ to any of the above questions, mean blood pressure measurements were assessed. In the 2003-04 cohort, the mean systolic and diastolic pressures were provided by NHANES. In the 2005-06 cohort, mean blood pressure measurements were derived, with support from data analysts at the Centers for Disease Control and Prevention, by averaging the last two (of three) blood pressure measurements taken. Individuals with a mean blood pressure ≥140 mmHg systolic or ≥90 mmHg diastolic were considered eligible for an anti-hypertensive medication, consistent with recommendations from the Joint National Committee (JNC)7, and were considered “untreated.”27
Indication for lipid-lowering medication (LLM; defined to be any statin, fibrate, niacin, or ezetimibe) was determined using recommendations put forth by the National Cholesterol Education Panel/Adult Treatment Panel (ATP) III. 28-29 Persons already taking a LLM, assessed using the Lexicon Plus® medication data file, were assumed to have an established indication for treatment, and identified as “treated.” Among persons not taking a LLM, we assessed eligibility for treatment.28
Individuals were categorized by cardiovascular risk: high, moderately high, moderate, and low. LDL levels were then assessed to determine appropriate cutpoints at which a LLM would be considered. The high risk group included individuals with coronary heart disease (CHD), assessed through self-report of coronary artery disease, myocardial infarction, or angina pectoris, and CHD-risk equivalents (e.g., diabetes, peripheral artery disease, and symptomatic carotid artery disease). Diabetes was assessed using self-report and fasting blood glucose levels.30 Peripheral artery disease was defined as an ankle-brachial index of <0.9 mm Hg. Data to assess presence of abdominal aortic aneurysm, a CHD risk equivalent, were not available.
In individuals without CHD or a CHD risk equivalent, we discriminated risk by assessing for the presence of major risk factors of CHD (other than LDL) and calculating a Framingham Risk Score (FRS).28 Major CHD risk factors include: age (men ≥45 years, women ≥55 years), smoking status, hypertension, high-density lipoprotein (HDL) level <40 mg/dL, and family history of premature CHD. For persons with 2 or more risk factors, we calculated their FRS. Individuals with an FRS >20% were included in the high risk group, those between 10% and 20% in the moderately high risk group, and those <10% in the moderate risk group. Individuals with 0 or 1 major risk factor were considered to be low risk. FRS was not calculated for individuals aged ≥79 years with 2 or more risk factors, as the FRS is not validated in this group. Persons with data missing to determine cardiovascular risk were excluded.
Individuals within each risk group were considered to have an indication for a LLM, and thus “untreated,” if their LDL was ≥100 mg/dL in the high risk group, ≥130 mg/dL in the moderately high risk group; ≥160 mg/dL in the moderate risk group; and ≥190 mg/dL in the low risk group. For those aged ≥79 years without known CHD or a CHD risk equivalent (and no FRS), we set the LDL threshold for which a LLM would be indicated at 160 mg/dL.
The primary independent variable of interest was USOC. Presence of a USOC was determined by self-report of: “do you have a place you usually go when you are sick or need advice about your health.” Respondents who answered “yes” were additionally asked to identify the place they most often go to seek care and categorized into: USOC-yes [doctor's office or HMO (private) or, health center or hospital outpatient department (public)], and USOC-no (no usual source of care or emergency department).
Sociodemographic covariates included: age, sex, race and ethnicity, education level, insurance status, and poverty income ratio (PIR). Insurance status was stratified into private, public (including Medicaid and individuals with exclusively Medicare or another government program), and no insurance. PIR was defined as the ratio of total family income to the family's household size-adjusted poverty threshold.
Clinical characteristics associated with an individuals’ cardiovascular health status were assessed. These included self-report of: hypercholesterolemia (assessed only in subgroup of individuals with an indication for anti-hypertensive therapy), hypertension (assessed only in subgroup of individuals with an indication for LLM), diabetes, and coronary heart disease.
We describe the sociodemographic and clinical characteristics of individuals with an indication for treatment of hypertension and hypercholesterolemia by USOC status. Weighted prevalence estimates were used to account for the survey's complex study design (including oversampling), survey non-response, and post-stratification, and multiplied by the 2005 US Census figure to estimate the number of individuals in each group.
We tested the unadjusted and adjusted association between USOC with being untreated for hypertension and hypercholesterolemia. We additionally tested the association of USOC and treatment status among a subset of patients with and without insurance coverage. We adjusted for variables significant in bivariate analyses, including: age, sex, race and ethnicity, insurance status, comorbid hypertension (in the group with an indication for LLM), co-morbid hypercholesterolemia (in the group with an indication for anti-hypertensive therapy), diabetes, and CHD. An interaction term between USOC and insurance was not significant, and thus excluded from the final models. Odds ratios, derived from multivariable logistic regression modeling, were converted to estimated prevalence ratios (PR's) given the high prevalence of the outcomes and to facilitate interpretation of results, using standard methods.31 To determine the joint effects of USOC and insurance status, we created four indicator variables: USOC-yes/Insurance-yes; USOC-no/Insurance-yes; USOC-yes/Insurance-no; and USOC-no/Insurance-no, and included these in the analysis with the above sociodemographic and clinical variables, to describe the risk of being untreated for hypertension and hypercholesterolemia. For all multivariable analyses, insurance status was dichotomized into yes/no, as we did not find a significant difference between public and private insurance on the receipt of medication therapy for hypertension or hypercholesterolemia in bivariate analyses.
SAS-callable SUDAAN software 10.0 (Research Triangle Institute 2001, Research Triangle Park, NC) was used to account for the nonrandom cluster sample design. The authors are solely responsible for the design and conduct of this study, all study analyses, the drafting and editing of the paper and its final contents. No extramural funding was used to support this work.
Among adults ≥35 years, 46.5% had an indication for anti-hypertension therapy (3,142 individuals; representing approximately 58.79 million persons) and 40.0% had an indication for a LLM (1,134 individuals; representing approximately 50.6 million persons). The proportion of adults who were untreated was high in both the hypertension (32.4%) and hypercholesterolemia (42.0%) groups.
Most adults reported having a USOC (Hypertension group: 93.1%; Hypercholesterolemia group: 93.6%), comparable to findings from other studies of patients with chronic illness.8, 32 When compared with adults with a USOC, adults without a USOC were less likely to have insurance (Hypertension group: 63.8% vs. 43.7% had private insurance; 28.9 vs. 16.3% had public insurance; 7.4% vs. 40.1% had no insurance, p<0.001). A similar distribution of insurance status was observed in the Hypercholesterolemia group (Table 1). Individuals without a USOC were less likely to be aware of their condition, either hypercholesterolemia or hypertension, and were less likely to report having co-morbid cardiovascular risk factors or disease.
Table 2 demonstrates the independent effects of USOC on being untreated for hypertension. In unadjusted analysis, adults with no USOC were significantly more likely to be untreated (unadjusted PR= 2.54, 95% CI: 2.28-2.76; p<0.001). After adjusting for sociodemographic and clinical characteristics, having no USOC remained significantly associated with being untreated (adjusted PR=2.43, 95% CI: 1.88-2.85; p<0.001). In multivariable analyses, now stratified by insurance status, no USOC was significantly associated with being untreated for hypertension among adults with insurance (PR=2.58; 95% CI: 1.88-3.08; p=<0.001) and without insurance (PR=1.81; 95% CI: 1.17-2.10; p=0.02). Table 3 demonstrates the main effects of USOC on receiving hypertension treatment. When compared with hypertensive adults who have both insurance and a USOC, adults with insurance but no USOC were more likely to be untreated (PR=2.58, 95% CI: 1.87-3.08; p<0.001), as were adults without insurance but with a USOC (PR=1.97; 95% CI: 1.38-2.52; p<0.001) and adults without either insurance or a USOC (PR=3.06, 95% CI: 2.37-3.39; p<0.001).
Similarly, among adults with an indication for treatment of hypercholesterolemia, USOC was significantly associated with being untreated (unadjusted PR= 2.06; 95% CI: 1.67-2.29; p<0.001; adjusted PR=1.79; 95% CI: 1.31-2.13; p<0.001). In multivariable analyses stratified by insurance status, among adults with insurance, USOC was non-significantly associated with being untreated (PR=1.65; 95% CI: 0.95-2.18; p=0.06). In adults without insurance, not having a USOC was significantly associated with being untreated (PR: 1.53, 95% CI: 1.40-1.57, p<0.001). Table 3 demonstrates that when compared with adults who have both insurance and a USOC, adults with insurance and no USOC as well as adults without insurance but with a USOC were more likely to be untreated (PR=1.64; 95% CI: 0.95-2.18; p=0.07; PR=1.58, 95% CI: 1.21-1.91; p<0.001, respectively).Adults without either insurance or a USOC had the greatest risk for being untreated (PR=2.53; 95% CI: 2.19-2.60; p<0.001).
In this recent, nationally representative sample, not having a USOC is independently associated with being untreated for two common cardiovascular risk factors, hypertension and hypercholesterolemia. This effect was observed among adults with and without insurance coverage. These findings support our hypothesis that USOC and insurance coverage have independent effects on the treatment of hypertension and hypercholesterolemia, and suggest the possibility that having a usual source of care might promote better preventive practices.
Hypertension and hypercholesterolemia are useful models for examining the influence of USOC on receipt of appropriate risk reductive medication treatment, as they are common and have clear and widely accepted guidelines for initiating medication therapy. For these cardiovascular risk factors we found that the risks of not receiving treatment were especially high for adults without a USOC. This observation may attest to the importance of the physician-patient relationship, beyond the benefit conferred by insurance coverage, in receiving appropriate preventive care. While more integrated and coordinated systems can and should be established to support productive physician-patient relationships (e.g., via providing financial incentives to support patient-centered medical homes), these systems rely on patients having access to a regular source of care.33-36
As with insurance status, the presence of a USOC varies by age, race, and health status.32 In our study, 7% of adults did not have a USOC, which is comparable to findings from other population surveys of adults with chronic illness.8 Reasons for lacking a USOC may be different from those contributing to lack of insurance.37 10, 26, 38-40 Hayword et al found that the majority of people (61%) did not have a regular provider by personal choice.37 The remaining 39% sited financial barriers, difficulty with finding providers who accepted new patients, and long travel distances, as reasons for not having a USOC. Our study was not able to assess subjects’ reasons for not having a USOC, though the addition of these questions to national databases may be important for guiding future efforts to facilitate access to a regular source of care.
Ultimately, as our country struggles to develop a health system that is capable of supporting high-quality chronic disease care management, different strategies may need to be applied to address the distinct issues of access to coverage and access to physicians.10, 26, 38-40 As demonstrated in Massachusetts, while the mandate was successful in increasing the number of insured, it did not increase the number of persons who reported having a regular provider.41-42 More explicit efforts to link persons with a regular source of care may help to improve CVD prevention, specifically by increasing opportunities to provide appropriate therapy for patients with hypertension and hypercholesterolemia.
Our study has some limitations. Data pertaining to the primary exposure variable, USOC, were limited. For example, it is unknown whether adults with no USOC were less inclined to seek medical attention or adhere to treatment recommendations for diagnosed conditions, or whether they experienced barriers to accessing a USOC. Such unmeasured factors may confound the relationship between USOC and treatment status. Secondly, we were not able to reliably assess indications for treatment in persons already receiving a medication. Individual preferences and physician clinical judgment may have contributed to adults not receiving treatment for either disease, although we were unable to assess this. Similarly, we were unable to assess treatment preferences among study subjects.
In summary, we found that having a usual source of care is strongly associated with receiving appropriate medication treatment for hypertension and hypercholesterolemia, even among adults with insurance coverage. Efforts to improve the delivery of chronic disease management may be aided by specific strategies to facilitate access to a regular source of care.
Erica S. Spatz, Robert Wood Johnson Clinical Scholars Program, Yale University School of Medicine, New Haven, CT, USA.
Joseph S. Ross, Department of Geriatrics and Palliative Medicine, Mount Sinai School of Medicine, New York, NY, USA and HSR&D Research Enhancement Award Program and Geriatrics Research, Education, and Clinical Center, James J. Peters VA Medical Center, Bronx, NY, USA.
Mayur M. Desai, Division of Chronic Disease Epidemiology, Yale University School of Public Health, New Haven, CT, USA.
Maureen Canavan, Division of Chronic Disease Epidemiology, Yale University School of Public Health, New Haven, CT, USA. Doctoral candidate, Yale University School of Public Health.
Harlan M. Krumholz, Robert Wood Johnson Clinical Scholars Program and Section of Cardiolovascular Medicine, Department of Medicine, Yale University School of Medicine; Section of Health Policy and Administration, Yale University School of Epidemiology and Public Health; Center for Outcomes Research and Evaluation, Yale-New Haven Hospital, New Haven, CT, USA.