Medicaid Expansion and Medicare-Financed Hospitalizations Among Adult Patients With Incident Kidney Failure
Abstract
Importance Although Medicare provides health insurance coverage for most patients with kidney failure in the US, Medicare beneficiaries who initiate dialysis without supplemental coverage are exposed to substantial out-of-pocket costs. The availability of expanded Medicaid coverage under the Patient Protection and Affordable Care Act (ACA) for adults with kidney failure may improve access to care and reduce Medicare-financed hospitalizations after dialysis initiation.
Objective To examine the implications of the ACA’s Medicaid expansion for Medicare-financed hospitalizations, health insurance coverage, and predialysis nephrology care among Medicare-covered adults aged 19 to 64 years with incident kidney failure in the first year after initiating dialysis.
Design, Setting, and Participants This cross-sectional study used a difference-in-differences approach to assess Medicare-financed hospitalizations among adults aged 19 to 64 years who initiated dialysis between January 1, 2010, and December 31, 2018, while covered by Medicare Part A (up to 5 years postexpansion). Data on patients were obtained from the Renal Management Information System’s End Stage Renal Disease Medical Evidence Report, which includes data for all patients initiating outpatient maintenance dialysis regardless of health insurance coverage, treatment modality, or citizenship status, and these data were linked with claims data from the Medicare Provider Analysis and Review. Data were analyzed from January to August 2022.
Exposure Living in a Medicaid expansion state.
Main Outcomes and Measures Primary outcomes were number of Medicare-financed hospitalizations and hospital days in the first 3 months, 6 months, and 12 months after dialysis initiation. Secondary outcomes included dual Medicare and Medicaid coverage at 91 days after dialysis initiation and the presence of an arteriovenous fistula or graft at dialysis initiation for patients undergoing hemodialysis.
Results The study population included 188 671 adults, with 97 071 living in Medicaid expansion states (mean [SD] age, 53.4 [9.4] years; 58 329 men [60.1%]) and 91 600 living in non expansion states (mean [SD] age, 53.0 [9.6] years; 52 677 men [57.5%]). In the first 3 months after dialysis initiation, Medicaid expansion was associated with a significant decrease in Medicare-financed hospitalizations (−4.24 [95% CI, −6.70 to −1.78] admissions per 100 patient-years; P = .001) and hospital days (−0.73 [95% CI, −1.08 to −0.39] days per patient-year; P < .001), relative reductions of 8% for both outcomes. Medicaid expansion was associated with a 2.58–percentage point (95% CI, 0.88-4.28 percentage points; P = .004) increase in dual Medicare and Medicaid coverage at 91 days after dialysis initiation and a 1.65–percentage point (95% CI, 0.31-3.00 percentage points; P = .02) increase in arteriovenous fistula or graft at initiation.
Conclusions and Relevance In this cross-sectional study with a difference-in-differences analysis, the ACA’s Medicaid expansion was associated with decreases in Medicare-financed hospitalizations and hospital days and increases in dual Medicare and Medicaid coverage. These findings suggest favorable spillover outcomes of Medicaid expansion to Medicare-financed care, which is the primary payer for patients with kidney failure.
Nearly 800 000 people in the US have kidney failure, with Black and Hispanic or Latino populations and those with low household incomes disproportionately affected.1–3 Among persons with kidney failure treated with dialysis, the period immediately after initiating dialysis carries substantial risk of mortality, frequent hospitalizations, infections, and cardiovascular events.4–6 Although mortality rates have declined in recent years, reported mortality rates among patients with incident kidney failure were 8% at 90 days and 22% at 1 year.7
Medicare is the primary insurer for individuals in the US aged 65 years and older as well as those younger than 65 with disabilities who receive Social Security Disability Insurance (SSDI). Medicare also provides health insurance coverage for most patients with kidney failure, and coverage begins at 91 days after initiating in-center hemodialysis or at the time of enrolling in training for home-based dialysis. In 2017, Medicare fee-for-service spending for all beneficiaries with kidney failure was approximately $36 billion (or 6% of total spending).1 However, Medicare beneficiaries who initiate dialysis without supplemental coverage (eg, Medigap plans, employer-sponsored retiree benefits, or Medicaid) are exposed to substantial out-of-pocket costs, and Medicare Part D prescription drug coverage requires premiums and cost sharing.8,9 As part of the Patient Protection and Affordable Care Act (ACA), states had the option of expanding Medicaid eligibility to adults with low household incomes, and as of April 2022, 38 states and the District of Columbia have done so.10 Medicaid expansion has had favorable outcomes for patients with kidney disease, including increases in health insurance coverage, Medicaid-covered preemptive listings for kidney transplantation, and 1-year survival after dialysis initiation.11,12 State Medicaid expansion decisions and Medicaid generosity (eg, levels of state Medicaid coverage) are associated with lower kidney failure incidence and increased use of an arteriovenous fistula or graft at dialysis initiation.13,14
In addition to providing assistance with Medicare premiums and cost sharing,15 Medicaid expansion may facilitate access to predialysis nephrology care for adult patients initiating dialysis,8 thereby preventing complications and reducing the number of Medicare-financed hospitalizations and hospital days immediately after dialysis initiation. These implications may be evident among adults with low household incomes eligible for Medicaid after the ACA and for those who were previously eligible for Medicaid but enrolled in the program after the ACA expansions, a phenomenon sometimes referred to as the woodwork or welcome mat effect. The aim of the study was to examine the implications of Medicaid expansion for Medicare-financed hospitalizations, health insurance coverage, and receipt of predialysis nephrology care among Medicare-covered adults aged 19 to 64 years with incident kidney failure.
In this cross-sectional study, we used a difference-in-differences approach to compare changes in the number of Medicare-financed hospitalizations, health insurance coverage, and receipt of predialysis nephrology care over time in Medicaid expansion vs nonexpansion states. The study population included persons aged 19 to 64 years with kidney failure who initiated dialysis between January 1, 2010, and December 31, 2018, while covered by Medicare Part A. The study period included 4 years during which patients initiated treatment before Medicaid expansion (2010-2013) and 5 years after expansion (2014-2018). Consistent with previous work, we considered expansion states as those that implemented the ACA’s Medicaid expansion from 2014 and afterward and excluded 5 states that extended Medicaid eligibility to adults with low household incomes between 2010 and 2013 (eTable 1 in the Supplement).16,17 Each state’s postexpansion period was defined by its own implementation date, which was January 1, 2014, for most states. The Brown University Institutional Review Board and the Centers for Medicare & Medicaid Services (CMS) Privacy Board approved the study protocol and waived the requirement for informed consent because only deidentified data were used. The study followed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline for cross-sectional studies.
We used data from the Renal Management Information System’s End Stage Renal Disease Medical Evidence Report (CMS 2728), which is completed for all people initiating outpatient maintenance dialysis regardless of health insurance coverage, treatment modality, or citizenship status.18 Because CMS 2728 includes patients’ primary mailing addresses, we geolocated patients into US Census tracts using ArcGIS spatial mapping software, version 10.5.1 (Esri).3,11,13,19 Hospitalizations were assessed by linking the CMS 2728 data to the Medicare Provider Analysis and Review, which includes information about all Medicare-financed hospitalizations, including primary diagnoses and number of hospital days. Data sets were linked using patients’ Medicare beneficiary identifiers. We included patients with both traditional Medicare and Medicare Advantage because the Medicare Provider Analysis and Review includes more than 90% of hospitalizations for enrollees in Medicare Advantage.20,21 The 2009 to 2013 American Community Survey data provided the poverty rate in each patient’s US Census tract.
The primary outcomes were the number of Medicare-financed acute care hospitalizations and number of acute care hospital days in the first 3 months, 6 months, and 12 months after initiation of dialysis. Secondary outcomes were dual Medicare and Medicaid coverage at 91 days after dialysis initiation, receipt of predialysis nephrology care, presence of arteriovenous fistula (AVF) or graft at dialysis initiation for patients undergoing hemodialysis, receipt of home dialysis, and dialysis type at initiation (hemodialysis vs peritoneal dialysis). We also assessed hospitalizations due to cardiovascular disease or infectious conditions using the US Renal Data System’s approach to classify these conditions.22 We attributed hospitalizations to the quarter of the patient’s date of dialysis initiation.
Data were analyzed from January to August 2022. We used a linear regression model with Huber-White robust SEs clustered at the state level. Covariates included age, sex, race and ethnicity, primary cause of kidney failure, presence of congestive heart failure, atherosclerotic heart disease, other cardiac disease, hypertension, diabetes, diabetic retinopathy, cancer, obesity (body mass index >30, calculated as weight in kilograms divided by height in meters squared), smoking status, alcohol dependence, and hemoglobin and serum albumin levels at dialysis initiation.11 The CMS 2728 specifies that a patient’s race and ethnicity should be collected using patient self-report at treatment initiation and was classified as Hispanic or Latino, non-Hispanic African American or Black, non-Hispanic Asian, non-Hispanic White, or non-Hispanic other race (American Indian or Alaska Native, Native Hawaiian or Pacific Islander, or other race). Consistent with previous work, for observations missing serum albumin and hemoglobin levels, we used the mean value of the covariates for nonmissing observations.11 All models included state and year-quarter fixed effects. Analyses were conducted in Stata, version 17 (StataCorp LLC) and used 2-tailed hypothesis testing with a significance threshold of P < .05.
We compared characteristics of persons with kidney failure aged 19 to 64 years who had Medicare Part A at treatment initiation vs those who did not during the study period to assess the generalizability of our findings. To assess the validity of the difference-in-differences study design and to test the robustness of the findings, we conducted several sensitivity analyses (eAppendix in the Supplement). First, we visually inspected preexpansion trends. Using quarterly data before 2014, we then tested the statistical significance of an expansion-by-time trend and separately used a categorical time specification. Second, we reran the analyses to include states that expanded Medicaid before January 1, 2014, or late-expanding states (eTable 1 in the Supplement). Third, we examined changes in patient characteristics over time by state expansion status to account for potential shifts in patient composition. Fourth, we used a Poisson model to examine changes in number of hospital days. Fifth, we ascertained the sensitivity of the results to inclusion and exclusion of hemoglobin and serum albumin levels in the risk-adjusted model and included missing hemoglobin and serum albumin levels as an indicator variable. Sixth, we modeled the postperiod as an event study (comparing annual changes in outcomes to a pooled preperiod), for which a state’s postexpansion period was defined by its own implementation date (eTable 1 in the Supplement). Seventh, in exploratory analyses, we examined whether there were differential changes in outcomes by age, sex, race and ethnicity, or area-level poverty (ie, living in a US Census tract where 20% or more of the population was living below the poverty threshold, which varies based on the size of the family and number of children in the household) by testing the significance of 3-way interactions among expansion status, time period, and each characteristic. In addition, to account for the competing risk of death, we calculated mortality rates within 3-month, 6-month, and 12-month periods after initiating treatment.
The study population included 188 671 adults aged 19 to 64 years who initiated dialysis while covered by Medicare Part A. Of this total, 97 071 resided in Medicaid expansion states (mean [SD] age, 53.4 [9.4] years; 58 329 men [60.1%] and 38 742 women [39.9%]; 13.3% Hispanic or Latino, 26.4% non-Hispanic African American or Black, 3.4% non-Hispanic Asian, and 54.5% non-Hispanic White individuals and 2.5% non-Hispanic individuals of other races), and 91 600 resided in nonexpansion states (mean [SD] age, 53.0 [9.6] years; 52 677 men [57.5%] and 38 923 women [42.5%]; 12.6% Hispanic or Latino, 40.2% non-Hispanic African American or Black, 1.0% non-Hispanic Asian, and 45.0% non-Hispanic White individuals and 1.2% non-Hispanic individuals of other races) (Table 1). The most common original reason for Medicare eligibility among both groups was disability insurance benefits (59.5% in expansion states, 51.9% in nonexpansion states) and disability and end-stage kidney disease (24.5% in expansion states, 29.7% in nonexpansion states).