Interruptions in Medicaid Coverage and Risk for Hospitalization for Ambulatory CareSensitive Conditions

Context Many persons in the United States experience interruptions in their health insurance coverage. Contribution This study of hospitalized California adults with Medicaid found an association between interruptions in coverage and a higher rate of hospitalization for ambulatory caresensitive conditions, such as heart failure, diabetes, and chronic obstructive pulmonary disease. Caution The study sample was limited to hospitalized patients, and some patients with interrupted coverage may have obtained private insurance. Implication Interruptions in insurance coverage were associated with hospitalization for ambulatory caresensitive conditions. Policies that reduce the interruptions in coverage might prevent some of these hospitalizations. The Editors Many U.S. citizens experience interruptions in health insurance coverage. A total of 85 million persons, or 38% of the U.S. population, younger than age 65 years were uninsured for at least part of a 3-year period (1). Low-income U.S. citizens are particularly at risk for periodic lack of insurance. Many poor persons move in and out of the Medicaid program with periods of being uninsured in between (2, 3). Medicaid reenrollment policies affect the number of beneficiaries who experience interruptions in their coverage. A shorter period for eligibility redetermination creates an administrative barrier to continuous coverage (4). Federal law requires that Medicaid eligibility be redetermined at least annually, but many states require this assessment at a shorter interval. In California, for example, adults need to redemonstrate their eligibility for Medicaid every 3 months. Research suggests that individuals with interrupted insurance coverage are less likely to receive primary care and preventive services (5). One potentially useful but as yet unexplored measure of morbidity and costs associated with interrupted Medicaid coverage is hospitalizations for ambulatory caresensitive conditions. Ambulatory caresensitive conditions, such as asthma, diabetes, and hypertension, are conditions that can often be managed with timely and effective treatment in an outpatient setting, thereby preventing hospitalization (6). Hospital admissions for these conditions reflect a decline in health status and, by association, the health consequences of access barriers. We performed a retrospective cohort study to determine whether interruptions in Medicaid enrollment are associated with an increased risk for hospitalizations in adults with ambulatory caresensitive conditions. Methods Data To conduct the analysis, the 1998 to 2002 California hospital patient discharge data available from the California Office of Statewide Health Planning and Development was linked with the Medicaid Monthly Eligibility File for the corresponding period from the California Department of Health Services. A deterministic match was done with social security numbers, sex, and year of birth available in both files, and a probabilistic match by using sex, date of birth, hospital identifier, and hospitalization dates was done on the residual to enhance the linkage. Judging by comparisons with separate Medicaid payment records, the California Department of Health Services estimated that more than 98% of Medicaid hospitalization records were successfully linked. Approximately 70% of the records were linked by using the deterministic method, and 27% were linked by using the probabilistic method (7). Furthermore, most records lacking a social security number needed for a deterministic match were for newborns, whom we excluded from this analysis. We were unable to correct for out-of-state hospitalizations of Medicaid beneficiaries. The California hospital patient discharge database includes a unique patient identifier and information about admission and discharge dates, patient demographic characteristics, diagnosis codes, and insurance status for the hospitalization. By linking the information available in the hospital discharge file with that available from the California Department of Health Services, we could confirm whether a hospitalized individual was in fact a Medicaid beneficiary and capture additional information on a monthly basis regarding Medicaid enrollment status, aid category, and whether the care was delivered through fee-for-service or managed care for all Medicaid beneficiaries, regardless of whether they were hospitalized. Furthermore, this linked file enabled us to capture hospitalizations for individuals who at one time may have had Medicaid coverage but did not have coverage at the time of a hospitalization. We limited our analysis to adults age 18 to 64 years. Outcome Measure We created longitudinal records of eligibility status and hospitalizations of any persons who were ever enrolled in Medicaid during the 5-year study period. We measured the duration of time within the study period from enrollment in Medicaid until the first hospitalization for an ambulatory caresensitive condition and the duration of time to subsequent hospitalizations thereafter. We classified hospitalizations in the patient discharge file as being for ambulatory caresensitive conditions on the basis of the definition provided by the Agency of Healthcare Research and Quality (AHRQ). We applied the AHRQ definitions of ambulatory caresensitive conditions, identifying hospitalizations in which the principal diagnosis International Classification of Disease, Ninth Edition, code was listed in the AHRQ 2001 guidelines (8). We have previously reported that these conditions comprise 26% of nonpregnancy-related hospitalizations for Medicaid beneficiaries in California (9). We compared the pattern of hospitalization rates for specific ambulatory caresensitive conditions between patients with continuous and those with interrupted Medicaid coverage. Because this pattern was quite similar, and for ease of interpretation and presentation, we followed the conventional practice of aggregating hospital admissions for any of the AHRQ ambulatory caresensitive conditions. Exposure Variable We modeled our primary exposure variable as a time-varying covariate indicating whether a beneficiary had or had not experienced an interruption of coverage. We identified an interruption of coverage when a monthly eligibility code after the first enrollment month was no longer present. The California Medicaid Monthly Enrollment file includes a code for Healthy Families, the California State Children's Health Insurance Program (SCHIP). Healthy Families allows persons up to the age of 19 years to qualify for Medicaid-type benefits in California but at somewhat higher income levels. For the purposes of our analysis, we considered enrollment in Healthy Families as a form of Medicaid coverage and did not consider it to be an interruption in coverage if an individual changed between these 2 programs over time. We characterized all periods before the interruption as continuous and those after the interruption as being discontinuous. Potential Confounders We measured several characteristics of beneficiaries that could influence their risk for a hospitalization for an ambulatory caresensitive condition as well as their risk for interrupted Medicaid coverage. These included demographic characteristics, Medicaid aid category, Medicaid health care delivery model, and forms of insurance other than Medicaid. Many of these variables are used to determine payment and were therefore complete in the data set. However, 68807 beneficiaries (1%) had missing information on race/ethnicity and were classified with those reported as other. Beneficiary demographic characteristics and Medicaid aid category provide an estimate of health status. We categorized aid category as Temporary Assistance to Needy Families (TANF), Supplemental Security Income (SSI), or other by using previously described algorithms (10). Medicaid eligibility through TANF is available to low-income children and their parents regardless of their health status. On the other hand, beneficiaries enrolled in Medicaid through the SSI program are eligible as a result of a chronic disability and therefore tend to be sicker on average than those eligible through TANF (11). From calculations using the Medi-Cal eligibility file data, we determined that most (83%) of the other group is composed of low-income persons whose incomes are too high for them to qualify for Medicaid but who subsequently do qualify for the medically needy aid category because of their acute out-of-pocket spending on health care services. The remainder of the other group is primarily women who are eligible on the basis of a pregnancy (12%) and persons who are eligible through one of several immigration-related programs (4%). The AHRQ provides an option for including the Elixhauser comorbid condition measure in the calculation of ambulatory caresensitive hospitalization rates (12). Incorporating diagnoses from administrative data in risk adjustment could introduce overadjustment if the comorbid conditions are a product of the same access-to-care barriers that result in hospitalizations for ambulatory caresensitive conditions. Nonetheless, we performed additional analyses incorporating the Elixhauser comorbid condition measure and found that its inclusion did not substantially affect our findings. Therefore, to simplify the presentation, we have chosen not to display these results. Except for the managed care indicator variable, all potential confounders were measured when beneficiaries enrolled in Medicaid. We classified Medicaid beneficiaries as being in managed care depending on whether they spent most of their enrollment time before a hospitalization for an ambulatory caresensitive condition in managed care. This was necessary because some beneficiaries changed between fee-for-service and managed care during their enrollment time. Statistical Analysis We performed descriptive analysis of the characteristics of Medicaid beneficiaries who did and