Medicaid Eligibility Expansions May Address Gaps In Access To Diabetes Medications

Abstract

Diabetes is a top contributor to the avoidable burden of disease. Costly diabetes medications, including insulin and drugs from newer medication classes, can be inaccessible to people who lack insurance coverage. In 2014 and 2015 twenty-nine states and the District of Columbia expanded eligibility for Medicaid among low-income adults. To examine the impacts of Medicaid expansion on access to diabetes medications, we analyzed data on over ninety-six million prescription fills using Medicaid insurance in the period January 2008–December 2015. Medicaid eligibility expansions were associated with thirty additional Medicaid diabetes prescriptions filled per 1,000 population in 2014–15, relative to states that did not expand Medicaid eligibility. Age groups with higher prevalence of diabetes exhibited larger increases. The increase in prescription fills grew significantly over time. Overall, fills for insulin and for newer medications increased by 40 percent and 39 percent, respectively. Our findings suggest that Medicaid eligibility expansions may address gaps in access to diabetes medications, with increasing effects over time.

Expanding access to prescription medications for diabetes is critical for improving US population health. Diabetes is one of the top ten causes of death and is a risk factor for heart disease, the top cause of death.^1–3 Many of the complications of diabetes can be prevented by the appropriate application of glucose-lowering drugs.^4–8 Yet not all people with diabetes receive the medications they need.^9–11 High out-of-pocket spending contributes to treatment nonadherence among patients with diabetes.^12–15 Uninsured people with diabetes may have difficulty obtaining needed care and often show elevated risk of poor glycemic control.^16–18

The average per patient cost of diabetes medications has risen in recent years, in part because of the increasing use of newer medications.^19,20 The number of medication categories for blood glucose control has swelled from three to eleven since the early 1990s. In 2013 the mean expenditure per patient for newer insulin analogues was almost double that for older formulations; likewise, the mean expenditure per patient for newer oral antihyperglycemic medications was almost double that for older oral medications.²¹

Despite their higher cost, these newer medications can carry important health benefits. For example, rapid- and long-acting insulin analogues provide equivalent glycemic control to large-dose conventional insulin therapy but with significantly less hypoglycemia in a non–intensive care setting.^22–24 Likewise, extended-release metformin is more effective than conventional formulations in improving glyco-metabolic control and lipid profile with a convenient dosing schedule.^25,26 Finally, glucagon-like peptide-1 (GLP-1) receptor agonists and sodium-glucose cotransporter-2 (SGLT-2) inhibitors have shown favorable effects on rates of hypoglycemia and body weight, as well as patients’ risk of cardiovascular events and mortality.^27–31 As a result, providing access to these costly newer medications could improve patients’ health.

The Affordable Care Act (ACA) originally required that all states expand eligibility for Medicaid to all adults with incomes below 138 percent of the federal poverty level. However, the US Supreme Court ruled that Medicaid expansion would be voluntary for the states.^32,33 Ultimately, twenty-five states expanded Medicaid eligibility in January 2014, and twenty-nine states and the District of Columbia did so in either 2014 or 2015.

These expansions were associated with an increase in the number of Medicaid prescriptions per enrollee and a drop in cost-related prescription nonadherence.^34–36 They also improved access to primary care among newly insured patients, which translated into increased health care use.^37–41

A prior study showed increases in the numbers of diabetes prescriptions filled using Medicaid insurance after Medicaid eligibility expansions and showed that Medicaid insurance did not crowd out other types of insurance to a great extent during the first fifteen months.⁴² Notably, diabetes prescriptions increased more than those in any other clinical category considered in that study. That study did not provide estimates by age and sex, as our study does. Another study measured increases in the prescribing of diabetes prescription drugs among people with one or more chronic conditions who gained Medicaid coverage in the period January 2012–December 2014.³⁴ This study focused on changes in prescription drug use over time among patients who had already filled prescriptions at baseline.

We are not aware of any studies that measure the additional Medicaid diabetes prescriptions filled during the first twenty-four months of the Medicaid eligibility expansions, or that report how the expansions affected the use of specific classes of diabetes medications. A study of specific drug classes would help define the health benefits associated with the expansions. A substantial increase in the use of newer medications would imply that the expansions helped resolve the slow diffusion of innovation to low-income patients with diabetes, possibly improving their health.^43,44

Improving access to diabetes medications, including newer ones, has the potential to influence the health of people living with diabetes for decades to come.⁸ Therefore, to inform ongoing policy discussions about expanding Medicaid eligibility in additional states or rolling back the expansions in other states, we assessed the impact of the expansions on the use of diabetes prescription medications filled using Medicaid insurance during the first twenty-four months after the expansions.We present estimates of the changes in diabetes prescriptions filled after the expansions by type of medication and patients’ sex and age. We used the estimates by age to conduct multiple checks of the data. Finally, we conducted a trend analysis to examine whether the changes associated with the expansions grew over time. Our study contributes to the literature on the implications of the expansions for patients with chronic conditions.

Study Data And Methods

STUDY DESIGN

We used a quasi-experimental difference-in-differences design to distinguish changes in diabetes prescription fills related to Medicaid eligibility expansions from temporal trends. Specifically, trends in diabetes prescription fills before versus after the expansions (the first difference) were compared in states with versus those without such expansions (the second difference). The pre-intervention period was January 2008–December 2013, and the postintervention period was January 2014–December 2015. We defined expansion states as those twenty-nine states (and the District of Columbia) that expanded Medicaid eligibility in 2014 or 2015, and we classified the other twenty-one states as nonexpansion or control states. Online appendix exhibit A1 provides additional details on the classification of states.⁴⁵

DATA

We measured fills of diabetes prescriptions using a large and representative administrative data set, the IQVIA Xponent data. The data captured prescription fills in all fifty states and the District of Columbia over eight years, including more than ninety-six million diabetes prescription fills for patients ages 20–64 paid for by Medicaid insurance. We tabulated these data by year, quarter, and state, as well as patients’ age group and sex. We combined these data with intercensal population data estimates,⁴⁶ and quarterly unemployment rates for each state from the Bureau of Labor Statistics.⁴⁷ We also used data for 2013–14 from the National Health and Nutrition Examination Survey to calculate the prevalence of diabetes by age group.⁴⁸

STATISTICAL ANALYSIS

We used the difference-in-differences method to model changes in diabetes prescriptions filled using Medicaid insurance after Medicaid eligibility expansions for states with versus those without such expansions. To account for the fact that the number of prescriptions increases along with the population, we used negative binomial models in which current population was the exposure variable.⁴⁶

We report the effects associated with the expansions as changes in prescription fills per 1,000 population per year (that is, average marginal effects per 1,000 population).⁴⁹ Appendix exhibit A2A provides additional details.⁴⁵

Our outcomes of interest were prescription fills for metformin (extended-release and regular), a first-line treatment for non-insulin-dependent type 2 diabetes; insulin (rapid- and longacting insulin analogues and regular insulin), a treatment for type 1 and insulin-dependent type 2 diabetes; three classes of newer oral medications (dipeptidyl peptidase [DPP]-4 inhibitors, GLP-1 agonists, and SGLT-2 inhibitors); and all other classes of diabetes medications. Prescriptions for all other drug classes were grouped together since they are not first-line agents, are not newer drugs, and were not used as frequently as other classes.We also analyzed the total numbers of diabetes prescriptions filled.

We clustered standard errors at the state level to account for the state-level nature of Medicaid eligibility expansions.We addressed possible residual confounding by adjusting for year by quarter indicator variables, state indicator variables, the age and sex of the person filling the prescription, and quarterly state-level unemployment rates.

We also conducted specification checks such as testing for parallel trends in Medicaid expansion versus nonexpansion states before the expansions, using linear and nonlinear specifications. We conducted a number of robustness checks. These included stratifying the data by age to compare changes in Medicaid diabetes prescription fills after Medicaid eligibility expansions with age-specific diabetes prevalence, estimating changes separately for 2014 and 2015, and examining whether quarterly changes after Medicaid expansions grew over time. We also examined whether the gap in Medicaid diabetes prescription fills between residents of expansion states and those of nonexpansion states shrank as expected once patients became eligible for Medicare at age sixty-five, omitted data from before 2011, and excluded states that expanded Medicaid eligibility before or after January 2014. Appendix exhibit A2A provides additional details on these analyses.⁴⁵

All analyses were performed using Stata/MP, version 14.

LIMITATIONS

Our study had several limitations. First, we were not able to track people over time. Instead, we analyzed data at the age-sexstate level across different time periods.

Second, patients’ race and ethnicity were not reported in the IQVIA data and therefore these variables were not included in our analyses.

Third, approximately 15 percent of retail pharmacies did not share their prescription fills data with IQVIA. Missing data were imputed by IQVIA using validated methods.⁵⁰

Fourth, nonretail prescriptions and mailorder prescriptions were outside the sampling frame. If Medicaid eligibility expansions also increased prescription fills at federally qualified health centers or mail-order prescription fills, our estimates would be underestimates of the total effect.

Fifth, we evaluated the association between Medicaid eligibility expansions and diabetes prescription fills in states with expanded Medicaid eligibility. Our findings might not be generalizable to a nationwide expansion of Medicaid eligibility.

Finally, ours was an observational study, and we therefore cannot rule out the possibility that other changes also accounted for or contributed to our results.

Study Results

States that did and those that did not expand Medicaid eligibility during 2014–15 appeared similar in several population-level characteristics in 2010, the year of the ACA’s passage (exhibit 1).

EXHIBIT 1.

Average characteristics in 2010 of states that did and did not expand eligibility for Medicaid under the Affordable Care Act

Characteristic	Nonexpansion states	Expansion states	p value of difference
Prevalence of diagnosed diabetes	7.96%	9.60%	0.06
Mortality per 100,000 people	829.57	826.60	0.93
Population	6,161,336	5,887,206	0.89
Male	49.20%	49.46%	0.25
Hispanic	11.53%	9.11%	0.40
Black	10.20%	12.55%	0.46
Older than age 65	13.53%	12.84%	0.15

SOURCE Authors’ analysis of data from the Census Bureau, the Centers for Disease Control and Prevention, the National Center for Health Statistics, and the National Vital Statistics System.

NOTE Twenty-nine states and the District of Columbia had expanded Medicaid eligibility by the end of our sample period.

Prescription fills for diabetes medications showed a slightly increasing trend before the ACA Medicaid eligibility expansions, in both expansion and nonexpansion states (exhibit 2). Appendix exhibit A3 shows the trends by medication class.⁴⁵ For each outcome and age group, we could not reject the null hypothesis that trends in our outcomes of interest were similar in these two groups of states before 2014; see Appendix exhibits A4B and A4C.⁴⁵ Additionally, an analysis of the annual gap in prescription fills between expansion and nonexpansion states showed a flat trend before 2014 and a break in that trend in 2014 (appendix exhibit A4D).⁴⁵

EXHIBIT 2.

Diabetes prescription fills using Medicaid insurance per 1,000 population ages 20–64, in states that did and did not expand eligibility for Medicaid

SOURCE Authors’ analysis of data from IQVIA. NOTE Most of the states that expanded Medicaid eligibility among low-income, nondisabled adults in 2014 or 2015 did so in the first quarter of 2014.

In 2014–15 Medicaid eligibility expansions were associated with increases of thirty Medicaid prescription fills for diabetes medications per 1,000 population among adults ages 20–64 (exhibit 3). We observed larger estimates for the increases in fills in 2015 than in 2014. When we divided the quarterly increase in fills into an intercept and a slope, we found that the slope was positive and significant—which indicates that the changes after Medicaid eligibility expansions grew over time (appendix exhibit A2D).⁴⁵

EXHIBIT 3.

Additional increases in annual Medicaid diabetes prescription fills per 1,000 population ages 20–64 associated with Medicaid eligibility expansions during 2014–15

		Difference-in-differences estimates
		Average annual change, 2014–15		Change in 2014		Change in 2015
	Baseline fills	Increase	95% CI	Increase	95% CI	Increase	95% CI
All patients	73.05	29.93	(21.40, 38.45)	24.21	(17.4, 31.39)	35.93	(25.62, 46.25)
Men	58.73	23.98	(17.42, 30.54)	19.19	(13.66, 24.72)	29.40	(21.70, 37.20)
Women	87.22	31.52	(21.77,41.26)	25.89	(17.66, 34.12)	37.40	(25.63, 49.17)
MOST COMMON TYPES OF DIABETES MEDICATIONS
Insulin and insulin analogues	23.21	9.35	(6.59, 12.11)	7.73	(5.44, 10.20)	11.40	(7.69, 14.39)
Metformin	29.13	12.17	(8.71, 15.63)	9.88	(6.95, 12.81)	14.58	(10.39, 18.77)
NEWER DIABETES MEDICATIONS
Rapid-acting insulin analogues	6.13	2.65	(1.87, 3.42)	2.18	(1.55, 2.80)	3.14	(2.18, 4.10)
Long-acting insulin analogues	12.10	4.54	(3.16, 5.92)	3.79	(2.66, 4.63)	5.32	(3.62, 7.10)
Extended-release metformin	3.05	1.59	(1.10, 2.70)	1.24	(0.80, 1.67)	1.95	(1.38, 2.53)
DPP-4 inhibitors, GLP-1 agonists, and SGLT-2 inhibitors	5.16	1.51	(1.60, 1.97)	1.13	(0.71, 1.54)	1.91	(1.37, 2.45)

SOURCE Authors’ analysis of data from IQVIA. NOTES Twenty-nine states and the District of Columbia had expanded eligibility for Medicaid by the end of our sample period. Baseline fills are those in 2013, measured in states that subsequently expanded eligibility for Medicaid. Difference-in-differences estimates were adjusted for year by quarter indicator variables, state indicator variables, patient’s age group and sex, and quarterly state-level unemployment rates. All changes were significant (p < 0:01). 95% confidence intervals are in parentheses. DPP is dipeptidyl peptidase. GLP is glucagon-like peptide. SGLT is sodium-glucose cotransporter.

Newer medications (rapidand long-acting insulin analogues, extended-release metformin, DPP-4 inhibitors, GLP-1 agonists, and SGLT-2 inhibitors) accounted for about one-third of the increase in prescriptions (exhibit 3). This likely represented an increase in the uptake of newer medications among patients who previously lacked insurance. In the IQVIA data in 2013, 15 percent of diabetes prescriptions filled using cash were newer medications, compared with 35 percent, 37 percent, and 38 percent filled using Medicare, private insurance, and Medicaid, respectively. The lower uptake of newer medications among uninsured patients is consistent with the fact that these medications required substantially higher out-of-pocket spending at the time of the Medicaid eligibility expansions.^21,51

All findings remained qualitatively unchanged in additional robustness checks, in which we eliminated states that expanded Medicaid eligibility before 2014, eliminated all states that expanded Medicaid eligibility in months other than January 2014, or omitted data from before 2011. Results of these analyses are in appendix exhibits A2E and A2F.⁴⁵

The relationship between Medicaid eligibility expansions and Medicaid prescription fills for diabetes medications declined dramatically after patients reached age sixty-five, as expected. The increase in prescription fills was 82 percent smaller for people ages 65–69 than for people ages 60–64, despite the fact that the two groups had identical diabetes prevalence (exhibit 4).

EXHIBIT 4.

Prevalence of diabetes in 2013–14 and increase in Medicaid diabetes prescription fills per 1,000 population in 2014–15 associated with Medicaid eligibility expansions, by age group (years)

SOURCE Authors’ analysis of data from IQVIA and the National Health and Nutrition Examination Survey. NOTE 2013–14 are the years just before and during Medicaid eligibility expansions, for most of the twenty-nine states (and the District of Columbia) that had expanded eligibility for Medicaid by the end of our sample period.

Among people younger than age sixty-five, those in age groups with a higher prevalence of diabetes experienced larger increases in treatment (exhibit 4 and appendix A5).⁴⁵ The correlation between diabetes prevalence and changes in Medicaid prescription fills for diabetes medications among people ages 20–64 was 0.98 (p < 0:01).⁵² The results (shown in appendix exhibit A6)⁴⁵ were similar when, as a robustness check, we included only patients with diagnosed diabetes in the NHANES analysis.

Discussion

This study analyzed the associations between Medicaid eligibility expansions and Medicaid prescription fills for diabetes medications by patients’ age and sex and by medication category. We used a large, representative administrative data set that captured over ninety-six million Medicaid prescription fills for diabetes medications in retail outlets in the period January 2008–December 2015. The analysis accounted for changes in population and many possible confounders. Our results imply that an average of thirty additional Medicaid prescriptions for diabetes medications were filled annually per 1,000 population in states that expanded Medicaid eligibility.

Age groups with higher prevalence of diabetes before the ACA, such as ages 55–59, showed larger increases in diabetes prescription fills after Medicaid eligibility expansions. In addition, increases in fills after the expansions were much smaller among people ages sixty-five and older. Because Medicaid is a payer of last resort, eligibility for Medicaid was expected to have a smaller impact among patients who were also eligible for Medicare.

We found that annual prescription fills for insulin and metformin using Medicaid insurance each increased by approximately 40 percent after Medicaid eligibility expansions. In the period 2002–13, insulin’s mean price rose 197 percent— growth faster than that of any other drug class used to treat diabetes.^21,53 Estimated insulin spending per patient more than tripled, from $231.48 in 2002 to $736.09 in 2013.²¹ Patients without insurance would have been exposed to the full costs of insulin. Gaining Medicaid insurance would have significantly reduced out-of-pocket spending for insulin for previously uninsured patients, thereby facilitating uptake of the medication.

Furthermore, the sizable increase in the use of metformin suggests that many of the newly treated patients may have had recent onset of diabetes. This finding echoes those of previous analyses that linked Medicaid eligibility expansions with increased diabetes diagnoses.^54–57 Indeed, the drug class with the largest relative increase after the expansions (52 percent) was extended-release metformin, a reformulation of the first-line medication for type 2 diabetes.

More broadly, our data suggest that Medicaid eligibility expansions were associated with increased prescription fills for newer diabetes medications. This is important because these medications carry higher costs than the older formulations do but provide benefits such as reduced risk of hypoglycemia and reduced side effects.^22,23,26 Newer medications accounted for about one-third of the increase in Medicaid diabetes prescriptions after the expansions, in line with prior Medicaid prescribing patterns in expansion states.⁵⁸ This represents an increase in use of newer medications compared with uninsured patients.

Our findings point to the possible health effects of Medicaid eligibility expansions. In the past, changes in cost sharing for diabetes medications have been associated with changes in health outcomes for patients with diabetes.^59,60 An analysis by the Centers for Disease Control and Prevention found that each additional treated patient with diabetes can lead to a reduction of $4,330 (in 1997 US dollars, equivalent to about $6,394 in 2017 US dollars) in inpatient care costs because of prevented hospital admissions.⁶¹ These figures may underestimate the current health effects of treatment, given that improved treatment regimens are now available.^29,62 Indeed, a decline in diabetes-related hospitalizations was observed shortly after Medicaid eligibility expansions in states with high baseline uninsured populations.⁶³

We found that the changes in the use of diabetes medications associated with Medicaid eligibility expansions increased over time. Ausmita Ghosh and coauthors reported a 24 percent increase in Medicaid diabetes medications through the first quarter of 2015.⁴² We found a 33 percent increase by the end of 2014, within the confidence intervals implied by the standard errors reported in that study, and a 49 percent increase by the end of 2015. The increasing gap over time between states that did and did not expand Medicaid eligibility is apparent from exhibit 2 and is significant (appendix exhibit A2D).⁴⁵

Our study had a number of strengths. First, by using administrative data on prescription fills, we avoided issues of patient self-report bias. Second, these data provided a sufficient sample size to examine the treatment of specific conditions by patients’ demographic characteristics and type of medication. Third, because these data were collected as prescriptions were filled, our data were timely and provided eight months of additional follow-up, compared to existing studies.

Fourth, although states with Medicaid eligibility expansions may differ from other states in some respects, population-level factors that differ between the groups do not bias the results in a difference-in-differences analysis as long as trends between the groups would have remained parallel in the absence of an intervention. We presented several analyses indicating parallel trends before the expansions, which provides evidence in support of this assumption.

Finally, we adjusted for state and year by quarter indicator variables, patient age and sex, and quarterly changes in unemployment on the state level to address residual confounding.

Conclusion

This study provides policy makers with new information about the potential benefits of continuing financial support for expansions of Medicaid eligibility. Our findings by drug class suggest that these expansions helped address some of the gaps in access to newer medications for low-income patients. An increase in access to newer medications may have important health effects, because the use of these medications has been linked with improved diabetes control and reduced symptoms in both clinical trials and observational data.^22–28 Furthermore, over a third of the additional diabetes Medicaid prescriptions associated with Medicaid eligibility expansions were for metformin, the first-line oral medication to treat diabetes that is not yet insulin dependent. Improvements in population health that are attributable to improved access to diabetes treatment, including the timely treatment of early-stage disease, could also justify some of the cost of expanding Medicaid. Finally, our study provides new evidence that the increases in treatment associated with Medicaid eligibility expansions can grow over time. ■

This research was previously presented at the AcademyHealth Annual Research Meeting, New Orleans, Louisiana, June 25, 2017; and the University of Chicago Chronic Disease Center Research Symposium, Chicago, Illinois, October 31, 2017. Rebecca Myerson gratefully acknowledges research funding from the Agency for Healthcare Research and Quality (Grant No. 1R36HS023964–01). Elbert Huang gratefully acknowledges research funding from the National Institute of Diabetes and Digestive and Kidney Diseases (Grant Nos. K24 DK105340 and P30 DK092949). The authors are thankful for the helpful suggestions of the anonymous referees.