Lipid-Lowering Medication Management in American Indians with Type 2 Diabetes: A Multi-Year View from a Rural Tribal Health System

Abstract

Background

American Indian Peoples have the highest prevalence of diabetes among all racial and ethnic groups. Atherosclerotic cardiovascular disease (ASCVD) is the leading cause of morbidity and mortality in people with type 2 diabetes. Lipid management, including statin medications, is recommended to reduce the risk of ASCVD for patients with type 2 diabetes.

Objectives

We described statin medication dispensing patterns and analyzed adherence trends by age group and intensity of statin therapy within the Choctaw Nation Health Services Authority (CNHSA) type 2 diabetes patient population. Our second objective was to compare the frequency and timing of lipid panels to current guidelines.

Methods

This was a retrospective secondary analysis of CNHSA electronic health record (EHR) data from 2017–2021 of patients who used CNHSA services and pharmacies. The adherence analysis included patients who were dispensed statins for >180 days. Patients were stratified based on age and statin intensity. The lipid panel analysis included labs obtained yearly and 4–12 weeks after a statin adjustment.

Results

Of the 8,330 CNHSA patients with diabetes medication, 69.6% were prescribed a statin. Of those, 45.0% were dispensed moderate-intensity statins exclusively; 23.7% were on high-intensity statins only. The age < 40 years group had the lowest adherence with mean PDC 0.69 (0.22). Yearly labs were completed for 85% of the patients in Year 1 after first statin dispense and 80%, 77%, and 71% in subsequent years. Of patients with adjustments, 13% had a follow-up lipid panel within 4–12 weeks after the first adjustment.

Conclusion

Statin medications were used by a large percentage of CNHSA patients with type 2 diabetes. Statin adherence was lowest in the younger age groups (< 40). Our findings provide insight into statin use, adherence, and laboratory findings. Future studies should examine barriers to adherence specific to the larger CNHSA population.

Background

More than 38 million people in the United States have diabetes, with type 2 diabetes accounting for over 90% of all diabetes diagnoses in adults.^1,2 American Indian Peoples have the highest prevalence of diagnosed diabetes among all racial and ethnic groups in the U.S.¹ Atherosclerotic cardiovascular disease (ASCVD), defined as coronary heart disease, cerebrovascular disease, or peripheral arterial disease of atherosclerotic origin, is the leading cause of morbidity and mortality in people with type 2 diabetes.³ This relationship is due both to common coexisting conditions for type 2 diabetes such as hypertension and dyslipidemia, and the inherent risk of diabetes itself.³ Numerous studies have shown the efficacy of controlling individual cardiovascular risk factors to prevent or slow ASCVD among people with diabetes.^3,4,5 The American Diabetes Association’s (ADA) 2023 Standards of Care in Diabetes recommend a four-pillar comprehensive approach to reduce the risks of diabetes-related complications, of which lipid management is the third pillar.³ Lipid management, combined with glycemic management, blood pressure management, and the use of glycemic agents with proven cardiovascular and kidney benefits, is recommended to help reduce the risk of diabetes complications such as cardiovascular and kidney complications.³

Many clinical trials have demonstrated the beneficial effects of statin therapy on ASCVD outcomes in patients with and without cardiovascular disease (CVD).^3,6 Consequently, the ADA recommends all adults with type 2 diabetes aged 40–75 years and no ASCVD use a moderate-intensity statin; however, during 2015–2018, nationally only 56.8% of adults met this requirement.¹ Additionally, high-intensity therapy should be considered in the context of additional ASCVD risk factors.³ These recommendations have remained consistent from the study time period to 2025 current ADA guidelines.^7,8 Medication adherence has been noted to be more crucial to treatment success than the actual treatment regimen.^9,10 For most medication regimens, adherence of 80% is needed for efficacy.¹¹ It is estimated that chronic medication adherence is 50%, and nonadherence accounts for approximately 50% of treatment failures nationally.^9,10 This demonstrates that while the use of statin medications in patients with diabetes is certainly important, adherence to these medications could be just as important to achieving positive outcomes.

Another important aspect of statin therapy management is monitoring lipid panels. The 2013 and 2018 Cholesterol Clinical Practice Guidelines from the American College of Cardiology/American Heart Association (ACC/AHA) recommend lipid panels 4–12 weeks after any adjustment in dose or medication to detect the maximum percentage change in low-density lipoprotein cholesterol (LDL-C).^8,12 Despite this recommendation, little is known about the frequency and timing of lipid panels in the United States among American Indian Peoples using Tribal Health Services. A 2023 study using National Health and Nutrition Examination Survey data, extensively examined lipid panels and the use of lipid-lowering medication among over 50,000 patients in general, but did not analyze the frequency of lipid panels.¹³ Some data exist for yearly lipid panel completion for patients on statin therapy, but few studies have focused on the lipid panels in the 4–12 weeks after starting or adjusting the dose of a statin. Data about American Indian Peoples and monitoring lipid panels can help guide further interventions and improve cardiovascular outcomes.

Objectives

The purpose of our study was to describe statin medication dispensing patterns and analyze adherence trends by age group (< 40, 40–75, >75 years) and by intensity of statin therapy (low, moderate, and high) within the Choctaw Nation Health Services Authority (CNHSA) type 2 diabetes population. We also sought to compare the frequency and timing of lipid panels to ACC/AHA guidelines.

Methods

Design

In this retrospective secondary data analysis, we examined CNHSA electronic health record (EHR) data between 2017 to 2021 to evaluate statin medication dispensing and adherence trends among American Indian adults diagnosed with type 2 diabetes. CNHSA serves the American Indian and Alaska Native population located in Southeastern Oklahoma within one hospital and eight clinics throughout the Choctaw Nation reservation.¹⁴ The dataset we examined included data for American Indian adults diagnosed with type 2 diabetes who used CNHSA services and pharmacies, were aged ≥18 years in 2017, and were dispensed medications from a CNHSA pharmacy. We excluded patients with end stage renal disease, other types of diabetes, or diabetic chronic kidney disease. We examined medications dispensed for at least 180 days consecutively, to allow for measurement of medication adherence. This study was approved by both the Choctaw Nation of Oklahoma Institutional Review Board and the University of Florida Institutional Review Board.

Measures

Medication data were stratified based on the intensity of statin dispensed (low, moderate, and high), as guidelines recommend different intensities of statins based on different patient criteria.³ As shown in Figure 1, low-intensity statins were pravastatin 10 mg and 20 mg, and simvastatin 10 mg. Moderate intensity statins were atorvastatin 10 mg and 20 mg, rosuvastatin 5 mg and 10 mg, simvastatin 20 mg and 40 mg, and pravastatin 40 mg and 80 mg. High-intensity statins were atorvastatin 40 mg and 80 mg, rosuvastatin 20 mg and 40 mg, and simvastatin 80 mg. Although simvastatin 80 mg is no longer recommended for use, a significant number of patients were prescribed this dose during our study time frame, and when it was recommended, it was considered a high-intensity dose (Figure 1).

Figure 1.

To assess medication adherence, we grouped patients by age (<40 years, 40–75 years, and >75 years) per ADA guideline recommendations. We evaluated adherence using the proportion of days covered (PDC). PDC is a measure of medication adherence that uses refill records to determine the number of days a patient has medication in their possession.¹⁵ PDC accounts for the possibility of early refills by moving extra days’ supply of medication forward to the first day that a patient would be without medication from the previous fill.¹⁵ Nine subgroups were analyzed, (low, moderate, and high intensity) for each of the three age groups.

Regarding lipid panel management, we assessed the presence of yearly lipid panels and timely follow-up labs after a statin adjustment. A lipid panel was defined as the presence of an LDL-C result in the patient’s EHR. A statin adjustment was defined as any change in dose or type of statin medication. For the analysis of yearly lipid panels, we included only patients on statin therapy for at least a year. A timely follow-up was defined as a follow-up lipid panel 4–12 weeks after an adjustment in statin therapy. These results were compared to ACC/AHA guidelines for the study period, which recommend yearly lipid panels and lipid panels within 4–12 weeks of a statin dose adjustment. Temporary changes to a patient’s statin therapy lasting for less than four weeks were not classified as dose adjustments. For the analysis of yearly lipid panels, we focused on the first dose adjustment for each patient and included only patients who started statin therapy before 2021. For the analysis of lipid panels within 4–12 weeks of statin adjustment, we focused on patients with their first adjustment before October 1, 2021 to allow 12 weeks to elapse and the opportunity for a lipid panel before the end of the study period.

For all analyses, we obtained descriptive statistics including mean, standard deviation, frequency, and percentage. Independent t-tests and mixed effect logistic regression were performed. All analyses were performed using R software (r-project.org). The threshold for statistical significance was a p-value of 0.05 or lower..

Results

Statin Use Analysis

There were 8,586 type 2 diabetes patients aged ≥18 years in 2017 with medication dispensing records in our dataset. After removing 256 patients with end stage renal disease, other diabetes, or diabetic chronic kidney disease, there were 8,330 patients. Of these, 5,797 (69.6%) were dispensed statin medications during the study time frame. At the time of their first statin dispensed in the study time frame, the patients were aged 19 to 90 with a mean age of 58.3 ± 12.2. The overwhelming majority (99.7%) were American Indian or Alaska Native. Over half (51.3%) were male and 48.7% were female. O1`2ne-fifth (19.9%) were single, 49.9% were married, 18.1% were divorced or separated, and 12.0% were widowed. Almost half of the patients taking a statin medication (45.0%) were exclusively on moderate intensity, 23.7% were only on high-intensity therapy, 5.5% were exclusively on low intensity, and the rest were on a combination of statin intensities throughout the time frame.

Adherence Analysis

For this analysis, we focused on the 4,298 patients on a single level of statin intensity during the study time frame. Most (84.4%) were aged 45–75, 7.2% were aged 18–45, and 8.3% were >75 years. Overall, 60.6% of the 4,298 patients were prescribed moderate-intensity statins, 32.0% were prescribed high-intensity, and low-intensity accounted for 7.4% of patients. The age group >75 had high adherence rates, with mean PDC rates of 0.84 ± 0.16, 0.82 ± 0.18, and 0.79 ± 0.24 for high, moderate, and low-intensity statin therapy, respectively. The age group 40–75 years had mean PDC rates of 0.81 ± 0.18, 0.79 ± 0.19, and 0.81 ± 0.19 for high, moderate, and low intensity, respectively. The lowest rates of adherence were in the age group < 40 years, whose adherence rates were 0.67 ± 0.23, 0.70 ±0.22, and 0.67 ± 0.26 for high, moderate, and low intensity, respectively. Across all intensity levels, the mean PDCs were 0.69 ± 0.22, 0.80 ± 0.19, and 0.82 ± 0.18 for the three progressively older age groups. The differences between the age < 40 group and the other two groups were statistically significant (p < 0.001).

Lipid Panel Management

In Year 1 after the first dispense of a statin, 85% of the patients had at least one lipid panel. In Year 2, 80% had at least one lipid panel, followed by 77% and 71% for Years 3 and 4, respectively. The decline over time was statistically significant (p < 0.001).

Of 4,208 patients, 1,499 patients had statin adjustments and remained on the new statin regimen ≥ 4 weeks. Of these, 78% had one statin adjustment, 16% had two, 4% had three, and 2% had 4 or more statin adjustments. Excluding 56 patients with the first statin adjustment within 12 weeks of the end of the study time frame, 13% had a follow-up lipid panel within the desired time window of 4–12 weeks after their first statin adjustments.

Discussion

The overall rate of patients dispensed statins (69.6%) in our sample was higher than most of the national Indian Health Service yearly targets for the Statin in Diabetes Government Performance and Results Act (GPRA) measure, which ranged from 37.5–61.9% during this time frame.¹⁶ This is higher than the rate reported for the general U.S. population with type 2 diabetes, which was 56.8% in 2015–2018.¹

We analyzed medication adherence among patients dispensed only one intensity of statin throughout the study time frame. Although adherence rates to statins were acceptable among all subgroups analyzed, only four of the nine subgroups (40–75 years, Low; 40–75 years, High; >75 years, Moderate; and >75 years, High) had an average PDC ≥0.80, which is largely considered the cutoff point for adherence to medication.^9,11 For the moderate and high-intensity statin categories, PDC increased as age increased. The intensity of statin does not appear to be closely related to adherence rates in our sample. This is consistent with findings in one systematic review examining adherence and persistence with statins, but literature on adherence rates and intensity is mixed.^17,18 Possible reasons for these adherence rates are the accessibility of medication services within the Choctaw Nation Health Services Authority, including 8 physical locations, and the ability to receive medications by mail.

The percentage of patients with consistent yearly lipid panels decreased the longer a patient was on statin therapy from 85% Year 1 to 71% in Year 4. For patients with a statin adjustment, approximately 1 in 8 had a follow-up lipid panel within the recommended time frame of 4–12 weeks after the first adjustment. A study among 210 patients from the University of Colorado Hospital found during a 3-year period, the mean number of lipid panels per patient was 3.01 ranging from 0–11.¹⁹ The literature is limited in reports of lipid panels within 4–12 weeks of a statin dose adjustment, but one study found that of 131,595 patients with a statin dose change, 24.7% had lipid panels within 4–12 weeks.²⁰ The higher percentage of lipid panels after a statin dose adjustment may be contributed to the use of statins for known ASCVD in that study population as opposed to primary or secondary prevention in type 2 diabetes.^3,20 Though ACC/AHA guidelines recommend this time frame, there is no clear guidance for management based on lipid panels.¹² The 2013 ACC/AHA guidelines shifted from a treat-to-target LDL-C approach to statin intensity chosen based on risk such as age, LDL cholesterol, and ASCVD risk.^8,12,13 The recommendation is lipid panels be completed to monitor adherence or safety.¹² This focus may explain why only a small portion of patients in this study had follow-up lipid panels within 4–12 weeks of a statin adjustment. If earlier follow-up was not prioritized, lipid panels may have been included with the follow-up appointment at the 6-month mark. The financial implications of these findings are far-reaching, reducing supplies, labor, and cost to the healthcare system in addition to reducing patient costs. Studies suggest annual monitoring of lipid panels not only raises healthcare cost, but also increases false positive results.^21,22 One study suggests testing every 3 years for patients stable on lipid-lowering therapy.²² Clinically, lipid panels play a small role in statin therapy management and reduced frequency may not impact changes to therapy.

Limitations

While prescription dispensing data are useful surrogates of medication adherence, they do not measure whether patients take the medication correctly at home. However, since CNHSA patients are required to request their prescriptions be filled each month rather than automatically as in some settings, the risk of patients picking up medications but not taking them at home is low. This study also did not address statin intolerance, which could impact adherence rates. Future analyses would benefit from addressing this barrier. Unfortunately, this study could not determine start dates for statin therapy. For this reason, there was no analysis of follow-up lipid panels within 4–12 weeks of initiation. In addition, only completed lipid panel requests were documented, so providers may have requested lipid panels that are not reflected in the dataset. There was an overlap between the study period and the COVID-19 pandemic, which could have negatively impacted the patient’s ability to come into the clinic for lab testing. End stage renal disease and diabetic chronic kidney disease were excluded from the prescription analysis before this specific study was designed, due to frequent medication dose changes.

Conclusion

This study examined statin medication dispensing patterns and adherence trends by age group and intensity of the statin in the CNHSA type 2 diabetes patient population. The primary outcome showed that statin medications are being used in a large percentage of this population, as recommended by both current and previous guidelines.^7,8,12 Our findings revealed that statin adherence was highest in the older age groups (40–75, >75). The secondary outcome comparing the frequency and timing of lipid panels to ACC/AHA guidelines revealed with each additional year a patient was on a statin, they were less likely to receive a lipid panel. Approximately 13% of patients received timely follow-up lipid panels within the 4–12 weeks of statin adjustment. However, some follow-up lipid panels may have been completed just outside the 4–12-week window and captured as lipid panels within the year instead, potentially leading to this low rate of follow-up lipid panels. Our findings provide insight into statin use, adherence, and lipid panel testing and suggest that applicable subsequent research would seek to identify barriers to adherence specific to the CNHSA population.

Table 1.

Adherence metrics (PDC-Proportion of Days Covered) and sample size stratified by age category and statin intensity.

Statin intensity	Age Category (years)
	18 – 39		40 – 75		76 +
	n	PDC, M(SD)	n	PDC ,M(SD)	n	PDC, M(SD)
High Intensity	52	0.68 (0.23)	1219	0.81 (0.18)	105	0.84 (0.16)
Moderate Intensity	241	0.70 (0.22)	2145	0.79 (0.19)	220	0.82 (0.18)
Low Intensity	20	0.67 (0.26)	263	0.81 (0.19)	33	0.79 (0.24)

PDC=proportion of days covered; SD=standard deviation

What was already known

• Statin medications are recommended for patients with type 2 diabetes to reduce the risk of complications such as ASCVD

• American Indian Peoples have the highest prevalence of diagnosed diabetes among all racial and ethnic groups

• Atherosclerotic cardiovascular disease (ASCVD) is the leading cause of morbidity and mortality in people with diabetes, both due to common coexisting conditions such as hypertension and dyslipidemia, and the inherent risk of diabetes itself

• Many clinical trials have demonstrated the beneficial effects of statin therapy on ASCVD outcomes

What this study adds

• Statin medication adherence increased with age. Lipid panel measurement frequency decreased the longer patients were on the medication

• Statin therapy adherence and dispensing patterns among American Indian Peoples by age and statin intensity within one Tribal Health System

• Lipid panel timing and frequency in our sample compared to recommendations from the American College of Cardiology/American Heart Association (ACC/AHA) guidelines