Determinants of elevated healthcare utilization in patients with COPD

A cross-sectional observational study was conducted at the Pulmonary Clinic of the Soroka University Medical Center, a tertiary care referral center with a catchment population of approximately 550,000. Ninety-five percent of patients in this clinic are enrollees of the Clalit Health Services (CHS), the largest health maintenance organization in Israel. The study was approved by the Institutional Ethics Committee (approval number 10283) as well as the committee of Clalit Health Services for extracting data from the database.

From March 2009 through December 2009, we prospectively recruited patients (n = 389) attending routine clinic appointments who met the following criteria: 1) enrollees of CHS, 2) age >35, 3) smoking history of ≥ 10 pack-years, 4) pulmonologist-diagnosed COPD. Exclusion criteria were: 1) other major pulmonary diagnoses, 2) concomitant disease expected to shorten life span to <3 years (determined from chart review by one of the investigators - NM), 3) exacerbations of COPD and/or hospitalization/urgent care visits within the month prior to recruitment (in order to obtain both clinical and HRQoL indices from stable patients). As a part of another study on HRQoL in COPD [13, 14], in a subset of 177 patients, data were collected on HRQoL as well as measures of sleep quality. As control subjects, patients without COPD were randomly selected from the database of CHS enrollees, matched 1:3 to the COPD patients (n = 1,167) by age, gender, primary-care clinic and area of residency.

Spirometric indices of lung function [15] were obtained within 6 months prior to the sentinel clinic visit from the patient's medical record at the pulmonary clinic, and included forced vital capacity (FVC) and forced expired volume in one second (FEV₁). Disease severity was staged according to the Global Initiative for Lung Disease (GOLD - 2006) [16], and % predicted FEV₁. Demographics including age, gender, body mass index (BMI), smoking status (current, ex-smoker), and pack-years smoking, were obtained from the patient's medical record at the pulmonary clinic. In the subset of 177 patients, indices of Health Related Quality of Life (HRQoL) and sleep quality were obtained using trained interviewers as described in another study of our group [13, 14] applying Hebrew translations of four-week recall questionnaires that included: 1) a generic questionnaire, the Health Utilities Index 3 (HUI3); 2) a disease specific questionnaire, the St. George's Respiratory Questionnaire (SGRQ); and 3) the Pittsburgh Sleep Quality Index (PSQI). Among this subset we collected data on socioeconomic status including: income relative to the Israeli average income, years of schooling, employment status and marital status. The presence of Comorbidities was obtained from CHS database, using the International Classification of Diseases, Ninth Revision (ICD-9) codes. The age-adjusted Charlson Comorbidity Score with Deyo Modification (CCI) [17] was calculated accordingly. Additionally, we assessed the presence of hypertension, depression, obstructive sleep apnea and pulmonary hypertension (that are not included in CCI and commonly found in COPD patients).

Information regarding annualized health care utilization was obtained for the five year period prior to the end of recruitment period (December 15, 2009) from the CHS financial database [18]. Under the obligatory Israeli National Health Insurance Law, all citizens have equal access to medical services. Physicians are generally paid a capitation fee and thus do not have economic incentive to increase healthcare consumption. Indicators of health care utilization included: hospitalization, emergency department visits, visits to specialists (consultations), surgeries including operative procedures such as cardiac catheterization and heart or spinal column surgeries, diagnostic procedures including CT scans, Ultrasound, MRI and spirometry, and medication according to the WHO classification system [19]. Although patients who had exacerbations of COPD and/or hospitalization/urgent care visits within the month prior to recruitment were excluded, our retrospective analysis over 5 years included patients who experienced exacerbation during these years but the data for the number of exacerbation were not available. Utilization costs estimates were based on a standardized price-list published by the Israeli Ministry of Health in 2009. Medication costs estimates were based on a price-list published by the CHS. All costs are expressed in US dollars ($) with an assumed exchange rate of 3.7 New Israeli Shekels per US dollar.

Data were analyzed using STATA software (ver 11.0, StataCorp, USA). Non-normally distributed variables were presented as median with 25-75 percentiles unless otherwise specified. Dichotomous indicator values were presented as proportions. Since health care utilization costs are not normally distributed, we stratified our COPD patients cohort into two subgroups [18]- the upper 25% (n = 98) who were the "most costly" patients and the "remaining" 75% (n = 291). Comparison between group medians was done using Mann-Whitney U test, and between proportions using Chi-square test. Regression was done using the least-squares technique. The null hypothesis was rejected at the 5% level.

Significant bivariate predictors of elevated health care utilization were put into a multivariate logistic regression. Independent variables included: age, gender, BMI, disease severity (percent predicted FEV₁, GOLD class), Comorbidities (number and category), age-adjusted CCI, smoking history (pack-yrs), HUI3, SGRQ, PSQI. In order to examine whether the model has predictive ability we obtained the area under the receiver operating characteristic (ROC) curve.

COPD patients consumed 3.4 times higher healthcare resources compared to controls. Since control subjects were randomly matched 1:3 to COPD cohort by age, it can be assumed that most characteristics are typical to this age range except for the elevated burden associated with COPD. Similar trends have been found previously [6, 7, 10]. Two studies conducted among Medicaid enrollees older than 45 in Maryland [7, 10] showed that that COPD patients consumed 1.33 time greater healthcare resources and had 1.8 times greater adjusted average number of inpatient claims compared to controls. Mapel et al. [6] found that healthcare utilization among COPD patients in New Mexico was approximately twice that of age and gender matched controls. Our results extend these previous ones showing that the same trends apply in a single-payer health system including various socioeconomic groups and extended age range. Our estimates may differ from those observed in other countries [1] due to variety of factors, among which the most important are: patients' selection method, differences in health system's payment schemes and in price-lists.

Each increase in age-adjusted CCI increased the odds of being a "most costly" COPD patient. The specific comorbidities predicting being in the "most costly" group were myocardial infarction, congestive heart failure, mild liver disease and diabetes. In the study of Lin and colleagues [10], determinants of health care utilization in COPD patients compared with others were diabetes with organ damage, peptic ulcer, congestive heart failure and mild liver disease. Thus, a number of the determinants of health care utilization in COPD patients compared with non-COPD patients also determine elevated health care costs within the COPD patient group. Even though our patients are from an extended age range with an older mean compared those of Lin et al, in both groups heart disease, diabetes and liver disease figure prominently as important comorbidities increasing health care utilization.

The connection between cardiovascular disease and COPD has been reported previously [6, 20, 21]. In our sample, these findings were reinforced by our findings that both congestive heart failure and myocardial infarction were independent predictors of being in the "most costly" group. Further, our results revealed increased utilization of cardiovascular drugs and increased costs related to cardiac surgeries among the "most costly" patients. Thus, it appears that managing care of COPD with concomitant cardiovascular disease should be one of the major foci for intervention in patients with COPD.

The presence of mild liver disease increased the odds of belonging to the "most costly" COPD patient. Although there is no single pathogenetic mechanism involved, chronic liver dysfunction may cause pulmonary manifestations because of alterations in the production or clearance of circulating cytokines and other mediators [22]. Further, this association may be related to the effect of smoking that is an important risk factor for COPD and is commonly reported by patients with advanced liver disease.

The co-presence of diabetes was an additional predictor for increased health care utilization. This result is consistent with previous studies showing that diabetes is a predictor of longer hospitalizations and adverse clinical outcomes in patients with acute exacerbations of COPD [5, 23]. In this regard, increased length of stay was a component of increased health care utilization for the "most costly" patients. From the database, we cannot determine precisely whether the "most costly" patients' hospitalizations were longer due to poor glucose control, but this could have been one contributor.

COPD is associated with significantly higher risk of having anxiety/depressive symptoms [24]. Recent studies had demonstrated that these symptoms among COPD patients were associated with an increased risk of COPD exacerbations and hospitalization [25, 26]. Hence, we expected that patients with COPD with elevated health care utilization would have been more likely to be diagnosed with anxiety and/or depression and would have thus consumed drugs to treat these conditions. Although our study did not include measures of anxiety and depression, we found that there was no significant difference between the most costly patient and the remainder in the prevalence of anxiety and depression, and the utilization of psychoactive drugs was low. This result may stem from the study population size, the willingness of physicians to address anxiety/depression in their COPD patients, or local practice patterns and needs further examination.

We found that the presence of concurrent OSA was not an independent predictor of elevated healthcare utilization. These results appear to be in conflict with the results of Shaya and colleagues [12] showing that the presence of OSA adds additional economic burden on beneficiaries who already have COPD. The discrepancy may relate to the fact that in neither study were attempts made to assess the true prevalence of OSA in COPD patients. However, the proportion of patients with OSA in the "most costly" group was greater in our study, but did not reach statistical significance. The sample of Shaya et al was considerably larger than ours, and it is possible that with larger numbers, our conclusions would have been the same as those of Shaya et al.

Interestingly, the severity of airflow obstruction was not an independent predictor of health care cost on multivariate analysis. It appears that once a patient has COPD, other factors, primarily comorbidities, determine health care utilization cost. Thus, the physiological impairment, while predicting mortality [5, 20], does not predict health care utilization independently of other comorbid conditions.

Our study demonstrated that as indices of health related quality of life (HRQoL) decline, annualized healthcare utilization increases. However, when the burden of specific comorbidities was taken into account, HRQoL per se was not a predictor of utilization. According to Sin and colleagues [20], the presence of comorbidities was associated with higher scores (implying worse HRQoL) on St George's Respiratory Questionnaire (SGRQ). Similar trends were found in another recent study of our group [13, 14]. Thus, it is most likely that HRQoL reflected the comorbidity burden.