Hospitalization Rates for Ambulatory Care–Sensitive Conditions in California Medicare HMOs

• Objective: To examine annual hospitalization rates for ambulatory care–sensitive conditions (ACSCs) among Medicare HMO beneficiaries. • Design: Cross-sectional descriptive study. • Setting and participants: Medicare beneficiaries aged 65 years and older continuously enrolled in 1 of 15 California Medicare HMOs from 1 January through 31 December 2001. • Measurements: Hospitalization rates overall and for each of 15 ACSCs (bacterial pneumonia, cellulitis, dehydration, gastric and duodenal ulcer, hypoglycemia, hypokalemia, severe ear/nose/throat infections, urinary tract infections, asthma/chronic obstructive pulmonary disease, congestive heart failure, diabetes, hypertension, seizure disorder, influenza, and malnutrition). The rate for the 15 ACSCs combined as well as acute, chronic, and preventable indices were also estimated. • Results: Of the 1.2 million Medicare beneficiaries enrolled in California HMOs during 2001, 24% were 80 years or older (range among plans, 15%–34%), 5% were African American (range, 1%–25%), and 6% were Medicaid-eligible (range, 3%–16%). Enrollees experienced a total of 315,503 hospitalizations in 2001 (267 per 1000), 22% of which were for an ACSC. ACSC hospitalization rates varied widely by plan and were higher among older enrollees, males, and those eligible for Medicaid. • Conclusion: ACSC hospitalization rates are easy to calculate based on administrative data. These rates can be used by individual plans as a method to screen for possible access and quality of care problems. Monitoring performance of Medicare HMOs continues to be a topic of considerable interest to policymakers and health plan administrators. A measure that has been suggested for tracking the performance of these plans is hospitalization rates for ambulatory care–sensitive conditions (ACSCs) [1]. This approach is based on the assumption that providing patients with timely and appropriate care in the outpatient setting will lead to reduced hospitalizations for ACSCs [2–4]. High ACSC admission rates may be indicative of problems with availability, access, or appropriateness of primary care, whereas low ACSC admission rates might reflect provision of effective primary care and preventive services [5]. Use of annual ACSC hospitalization rates to monitor access to care in Medicare HMOs builds on existing models developed for monitoring care for Medicare fee-for-service (FFS) beneficiaries. The rates are based on inpatient hospital encounter data that are routinely collected by Medicare HMOs. Tracking ACSC hospitalization rates over time is a practical tool that Medicare HMOs could use to identify clinical areas and subgroups of enrollees in further need of quality assessment and improvement. McCall et al [1] investigated the feasibility of using ACSC hospitalization rates to monitor the performance of Medicare HMOs. They hypothesized that ACSC hospitalization rates could be used for monitoring Medicare HMOs if 3 conditions are met: complete hospital data are available, ACSC hospitalization rates are considered to be valid measures of providing ambulatory care, and ACSC hospitalization rates are statistically reliable [1]. Using hospital inpatient encounter data for July 1997 to June 1998, McCall et al identified 305 Medicare HMOs with up to 255,520 enrollees and up to 54,009 discharges per HMO. They first evaluated the completeness of the inpatient encounter data and found it to be “sufficiently complete” based on a comparison of hospitalization rates for all conditions versus only ACSCs between Medicare HMO and FFS beneficiaries. Hospitalization rates were then calculated by age and sex and for ACSCs individually and collectively. They found that although Medicare HMO rates were consistently lower than Medicare FFS, the Medicare HMO From the School of Policy, Planning, and Development, University of Southern California, and theRAND Corporation, Santa Monica, CA, andWashington, DC. rates varied as expected with regard to geographic region and demographic characteristics. For example, higher ACSC hospitalization rates were observed in the Northeast and among those aged 85 years and older. Many studies have investigated inpatient utilization differences between Medicare FFS and HMO populations, with much of the difference attributed to healthier HMO enrollees (ie, favorable selection) and some to managed care practices of HMOs [6–14]. While differences in enrollee characteristics and utilization among Medicare HMOs are expected to be less than the “selection difference” between Medicare HMOs and FFS, these differences by plan have not been well documented. Understanding these differences by plan is important because rates of hospitalization for ACSCs have been shown to be sensitive to patient characteristics such as age, race/ethnicity, and income [4,15–19]. In the current study, we examine rates of hospitalization for 15 ACSCs using data on beneficiaries aged 65 years and older enrolled in Medicare HMOs in California during 2001. The specific objectives of the study were to compare annual hospitalization rates in Medicare HMOs for all conditions and for ACSC conditions by beneficiary characteristics and to estimate rates of ACSC hospitalizations at the plan level for Medicare HMOs.