Long-term Effectiveness of the National Diabetes Quality Assessment Program in South Korea

Diabetes is a major public health concern worldwide. According to the International Diabetes Federation, the prevalence of diabetes in individuals aged 20–79 years is projected to increase from 10.5% (536.6 million individuals) in 2021 to 12.2% (783.2 million individuals) in 2045 (1). In Korea, the prevalence of diabetes in adults aged ≥19 years was 13.9% in 2020. In addition, approximately one in four individuals has prediabetes, a condition that increases the risk of diabetes (2). This increase in the prevalence of prediabetes and diabetes can also lead to an increased prevalence of diabetes complications, which impose a considerable burden on individuals and the national health care system.

In many countries, including Korea, evidence-based guidelines on diabetes care standards have been developed with a focus on reducing the risk of diabetes complications. The guidelines recommend comprehensive diabetes care for individuals with diabetes, including achievement of glycated hemoglobin (HbA_1c), blood pressure, and cholesterol (ABCs) targets, and performance of examinations for eye and foot complications to prevent, or at least delay, the onset of diabetes complications (3–7). However, many individuals with diabetes do not achieve the target goals for indicators of diabetes care globally (8). In Korea, only 9.7% of individuals with diabetes met the ABCs target between 2019 and 2020 (2).

Effective and appropriate diabetes management requires timely intervention strategies by physicians as well as self-management by individuals with diabetes. For timely intervention, physicians need to perform regular tests for glucose and lipid levels to assess the achievement of certain targets and screening tests to detect complications early. However, it may be difficult for physicians to perform these tests in a primary care setting given the complex nature of diabetes management. In addition, differences in the quality of diabetes care due to physicians’ lack of knowledge about guidelines may affect the health outcomes of their patients (9). To improve current care, in 2011, the Korean government introduced the national diabetes quality assessment program (NDQAP), which provides financial incentives to primary care physicians for the achievement of process standards and quality in diabetes care. Immediately after the implementation of the policy, the performance of indicators of diabetes care quality, especially testing levels of glucose and lipids and examining for diabetes complications, improved dramatically in Korea (10). However, little is known about whether the achievement of NDQAP quality assessment indicators can prevent the development of diabetes complications in individuals with diabetes. Therefore, this study evaluated the long-term effectiveness of the NDQAP, a national program aimed at improving the quality of diabetes care in Korea, on diabetes complications and mortality in individuals with diabetes using the Health Insurance Review and Assessment Service (HIRA) database.

Korea has a mandatory single-payer national health care insurance system that covers ∼98% of the Korean population. The HIRA government agency has reviewed and assessed the suitability of all medical claims submitted by health care providers for reimbursement. The HIRA database contains sociodemographic characteristics, reimbursement claims, including the ICD-10 and Anatomical Therapeutic Chemical (ATC) codes, death, and quality assessment data.

We conducted a retrospective, population-based cohort study using the HIRA database. From 1 July 2012, to 30 June 2013, 1,079,033 individuals with type 1 or type 2 diabetes visiting a single primary care clinic were selected. Among them, we included 878,629 individuals aged 40–74 years with diabetes, excluding those aged <40 or ≥75 years. The proportion of individuals aged <40 years (2.2%) was relatively small compared with other age-groups, and strict glucose control and regular testing may not be recommended for older adults aged ≥75 years. Additionally, comorbidities and other factors related to aging may affect outcomes in adults aged ≥75 years. In accordance with HIRA’s regulation on data availability for research purposes, we obtained a sample of 400,000 individuals with diabetes (45% of the total population) using a randomized sampling method stratified by age (in 5-year intervals), sex, and region. After 16 individuals who died during the same period were excluded, 399,984 individuals with diabetes were included in the analysis. The study protocol was approved by the Institutional Review Board of Ajou University Hospital, Suwon, Republic of Korea (approval no. AJOUIRB-EXP-2021-660), and the requirement for informed consent was waived.

Since 2011, the HIRA has evaluated whether physicians in primary care settings manage individuals with diabetes according to the standards of process and quality and has provided incentives based on this. The NDQAP includes five quality assessment indicators as follows: regular outpatient visits, continuity of prescription for diabetes, regular testing of HbA_1c and lipid levels, and regular funduscopy examination (11). The definitions of the quality assessment indicators are shown in Supplementary Table 1. Each indicator was evaluated during the period from 1 July 2012 to 30 June 2013 (fundus examination was evaluated during the period from 1 July 2011 to 30 June 2013).

Financial incentives were provided when all criteria were met, based on the proportion of individuals who achieved the quality assessment indicators. The criteria for each quality assessment indicator were as follows: 1) regular outpatient visits; ≥90% of patients had visited the outpatient clinic at least once a quarter; 2) continuity of prescription for diabetes, with the number of prescription days ≥80% of the total period; 3) medical institutions that performed HbA_1c tests below the mean were excluded; 4) medical institutions that performed lipid tests or fundus examinations below 10% were excluded; and 5) 10% of medical institutions with a large number of duplicate prescriptions of the same ingredient antihyperglycemic agents or more than four ingredient groups were excluded. We defined high-quality institutions as clinics that received incentives according to the above criteria.

The main exposure was the achievement of each quality assessment indicator of the NDQAP. Additionally, we evaluated the number of quality assessment indicators achieved, the level of each quality assessment indicator, and whether individuals were managed in a high-quality institution. The number of quality assessment indicators achieved was categorized into four groups: 0–2, 3, 4, or 5. The level of each quality assessment indicator was assessed using the following criteria: 1) continuity of prescription: prescription days in a year, <290, 290–329, or ≥330; 2) HbA_1c test: number of measurements in a year, 0, 1, 2, or ≥3; 3) lipid test: the number of measurements in a year, 0, 1, 2, or ≥3; and 4) fundus examination: the number of measurements in 2 years, 0, 1, or ≥2.

We evaluated severe microvascular complications, cardiovascular complications, and all-cause mortality. Severe microvascular complications include proliferative diabetic retinopathy (PDR), end-stage kidney disease (ESKD), and amputation. Cardiovascular complications included hospitalizations for myocardial infarction (MI) and stroke. Severe microvascular and cardiovascular complications were defined using the ICD-10 and procedure codes (Supplementary Table 1). Dates of death were obtained from the National Death Registry (all participants were assigned a unique number). The follow-up time was from the index date (1 July 2013) to the date of the first occurrence of the outcome, the date of death from any cause, or the end of the study period (31 May 2021).

All prescribed drugs and diagnoses were retrieved from insurance claims lodged during the year within the 2 years prior to the index date of 1 July 2013. The history of comorbidities included MI, stroke, microvascular complications of diabetes, hypertension, dyslipidemia, and cancer. The prescribed drugs were classified using ATC codes for glucose-lowering drugs, antihypertensive drugs, statin drugs, and antiplatelet drugs (Supplementary Table 1).

Baseline characteristics are presented as the mean ± SD for continuous variables and as a number (%) for categorical variables. Kaplan-Meier curves were used to analyze the cumulative incidence of each outcome according to the number of achievement of quality assessment indicators. We used Cox proportional hazards models to evaluate the association between the achievement of quality assessment indicators and each outcome of interest using hazard ratios (HRs) and 95% confidence intervals (CIs) and adjusted for confounders such as age, sex, the history of the disease, and prescribed drugs.

To address the possibility of reverse causality, we conducted three sensitivity analyses to evaluate the association of achievement for each quality assessment indicator with risk of diabetes complications and all-cause mortality. First, individuals with severe comorbidities, such as PDR, ESKD, amputation, MI, stroke, or cancer within 2 years prior to the index date, were excluded (n = 339,388), as these individuals may have limited access to primary care institutions, and diabetes-related tests are likely to be neglected due to priorities for the treatment of other severe comorbidities. Second, we excluded any event that occurred within the first 2 years after the index date, as finding undiagnosed microvascular complications through diabetes-related tests, such as fundus examination, can be interpreted as causing complications. Finally, considering the continuity of the degree of achievement of quality assessment indicators, the analysis was conducted by adding data of quality assessment indicators after 2 years as a confounding variable (n = 311,519). All analyses were performed using SAS Enterprise Guide 7.1 software (SAS Institute, Cary, NC).

The study included 399,984 individuals with diabetes (mean age 59.9 years; 56.1% men) who visited a single primary care clinic. Most participants with diabetes (93.8%) visited clinics for the management of diabetes at least once every quarter. The proportion of individuals consistently prescribed glucose-lowering drugs was 81.8% (based on the medication possession ratio). The proportions of individuals who underwent HbA_1c and lipid tests at least once a year were 70.4% and 65.9%, respectively. However, the proportion of individuals who underwent fundus examination at least once in 2 years was relatively low (34.3%). The proportion of individuals who achieved all of the quality assessment indicators was 18.1% (Supplementary Table 2).

During the mean follow-up duration of 7.6 ± 1.8 years, PDR occurred in 20,054 (5.0%), ESKD in 6,281 (1.6%), amputation in 1,943 (0.5%), MI in 9,706 (2.4%), stroke in 26,975 (6.7%), and all-cause mortality in 35,799 (8.9%). Fig. 1 shows the risk of severe diabetes complications and all-cause mortality based on each quality assessment indicator. Achieving each quality assessment indicator had a lower risk of PDR, ESKD, amputation, MI, stroke, and all-cause mortality. Among the quality assessment indicators, continuity of prescription for glucose-lowering drugs was the strongest factor for reducing the risk of severe diabetes complications and all-cause mortality. However, fundus examinations performed at least once every 2 years were associated with a higher risk of PDR (HR 1.21; 95% CI 1.17–1.25). The associations between each quality assessment indicator and severe diabetes complications and all-cause mortality persisted even after adding other quality assessment indicators as confounding variables (Supplementary Fig. 1). We divided the participants into four groups based on achievement of regular outpatient visits and continuity of prescription. Regardless of the regular outpatient visits more than once a quarter, the achievement of continuity of prescription was associated with lower risk of severe diabetes complications and all-cause mortality (Supplementary Table 3).

When individuals with severe comorbidities at baseline were excluded, the associations of quality assessment indicators achievement with severe diabetes complications and all-cause mortality were stronger than the main results shown in Fig. 1. Additionally, the association between achievement of regular fundus examinations and the risk of PDR was no longer statistically significant (HR 1.00; 95% CI 0.96–1.04) (Supplementary Fig. 2).

Achievement of quality assessment indicators was associated with a higher risk of mild microvascular complications (Supplementary Fig. 3). However, when any event that occurred within the first 2 years after the index date was excluded, the overall estimated HRs decreased, and achievement of quality assessment indicators, except for fundus examination, was associated with a lower risk of diabetic neuropathy. Furthermore, the association between achievement of regular fundus examinations and risk of PDR was no longer statistically significant (HR 1.00; 95% CI 0.96–1.05) (Supplementary Fig. 4).

When adjusted for the quality assessment indicator after 2 years as an additional confounder, the overall pattern of association between achievement of quality assessment indicators and each outcome was similar to the main results shown in Fig. 1 (Supplementary Fig. 5).

Figure 2 and Supplementary Fig. 6 show the risk of severe diabetes complications and all-cause mortality based on the number of quality assessment indicators achieved. We discovered that as the number of achievement of quality assessment indicators increased, the risk of developed PDR, ESKD, amputation, MI, stroke, and all-cause mortality decreased. Achievement of all five quality assessment indicators showed the lowest risk of severe diabetes complications and all-cause mortality compared with the achievement of two or fewer. However, as the number of achieved quality assessment indicators increased, the risk of mild microvascular complications increased as well (Supplementary Fig. 7).

Figure 3 shows that the higher the achievement level for each quality assessment indicator, the lower the risk of severe diabetes complications and all-cause mortality. A longer duration of continuity in the prescription of glucose-lowering drugs was associated with a lower risk of severe diabetes complications and all-cause mortality. Individuals with diabetes who underwent HbA_1c and lipid tests more than twice a year had a lower risk of severe diabetes complications than those with diabetes who underwent tests once a year or never. For fundus examination, individuals with diabetes who underwent testing biennially had the lowest risk of severe diabetes complications and all-cause mortality.

Table 1 demonstrates the risk of severe diabetes complications and all-cause mortality according to whether individuals were treated in a high-quality institution. Among the study participants, 48.9% of those with diabetes were managed in high-quality institutions. Individuals who were managed in high-quality institutions had a lower risk of PDR (HR 0.82; 95% CI 0.80–0.85), ESKD (HR 0.77; 95% CI 0.73–0.81), amputation (HR 0.75; 95% CI 0.69–0.83), MI (HR 0.85; 95% CI 0.82–0.89), stroke (HR 0.86; 95% CI 0.84–0.88), and all-cause mortality (HR 0.96; 95% CI 0.94–0.98) than those who were not managed in high-quality institutions. In addition, among those who did not achieve overall quality assessment indicators, those who were managed in high-quality institutions had a lower risk of severe diabetes complications and all-cause mortality than those who were not managed in high-quality institutions. Individuals with diabetes who achieved all five quality assessment indicators and were managed in high-quality institutions had the lowest risk of severe diabetes complications and all-cause mortality (Supplementary Table 4).

To the best of our knowledge, this study is the first to evaluate the long-term effectiveness of the NDQAP in individuals with diabetes in primary care settings. Using the HIRA database, we found that the achievement of NDQAP indicators (regular outpatient visits, continuity of prescriptions for antihyperglycemic agents, regular testing of HbA_1c and lipid profiles, or regular funduscopy examination) was associated with a reduction in the risk of developing diabetes complications and all-cause mortality. The more indicators of care quality that were achieved, the lower the risk of developing diabetes complications and even all-cause mortality in individuals with diabetes.

The main goal of diabetes management is to prevent microvascular and macrovascular complications of diabetes. Thus, guidelines on diabetes care standards recommend the control of cardiovascular risk factors and regular screening for diabetes complications (3–7). However, far from these guidelines, most individuals with diabetes do not receive the expected comprehensive diabetes care for the prevention of diabetes complications. In the U.S., <60% of individuals with diabetes are tested for HbA_1c and lipid profile in primary care settings (12). Abdel-Rahman et al. (8) reported that ∼70% of individuals with diabetes underwent annual testing for HbA_1c, LDL cholesterol, or creatinine in Israel. In the current study, 30% of the study participants never underwent HbA_1c testing even once for 1 year, and 34% of individuals never underwent lipid testing during the same period. Moreover, 66% of individuals did not undergo a fundus examination during the evalutaionperiod. This finding indicates that the level of adherence to indicators of diabetes care quality, which are recommended by guidelines, is very low in real-world clinical practice settings.

To reduce this gap and improve the quality of diabetes care, national monitoring programs to evaluate care quality in primary clinics are the first step. As the importance of guideline-oriented care for individuals with diabetes is emphasized, an accurate assessment of the adequacy of diabetes care performed in institutions is also receiving more attention. In many countries, quality assessment indicators have been developed and implemented to monitor the quality of diabetes care (7,13–16). In the U.S., the Diabetes Quality Improvement Project, a comprehensive set of national measures for evaluation and quality improvement, was implemented (13). In the U.K., the National Institute for Health and Care Excellence recommends that individuals with diabetes receive nine annual care processes in primary care (measurements of HbA_1c, blood pressure, lipids, creatinine, albuminuria, and BMI, ascertainment of smoking status, and examinations for eye and foot) and monitor the indicators for improving the quality of diabetes care (7,16). Providing financial incentives to primary care physicians is one way to improve the quality of diabetes care (17,18). The monitored quality assessment indicators were used to quantify performance incentives. The U.K. government has implemented the Quality Outcomes Framework, a comprehensive national primary care pay-for-performance model that provides financial rewards for leading to performance on quality assessment indicators (19). The financial incentive model showed some improvements in the achievement of HbA_1c and cholesterol levels (20). In Canada, financial incentives also increase adherence to testing for all three monitoring indicators (HbA_1c, cholesterol, and eye examination) (21).

In Korea, the government began implementing the NDQAP in 2011, which monitors quality assessment indicators for diabetes care and provides financial incentives to providers in primary care settings (11). By implementing NDQAP, the performance of quality assessment indicators increased. In particular, the proportion of regular HbA_1c tests increased from 69.9% in 2011 to 87.4% in 2020. During the same period, the proportion of regular tests for lipid levels increased from 48.8 to 80.3% (11). In Korea, the rates of diabetes complications and all-cause mortality have decreased constantly, and NDQAP may have contributed to this reduction (22). The current study shows that individuals with diabetes who achieved diabetes quality assessment indicators had a decreased risk of severe diabetes complications and all-cause mortality. The achievement of a higher number of quality assessment indicators was associated with a higher risk for diabetic retinopathy, diabetic nephropathy, and diabetic neuropathy; however, these results may have been confounded by the screening effect. Early detection of mild complications through regular screening tests may delay or prevent the development of severe complications. In addition, a fundus examination performed at least once every 2 years was associated with a higher risk of PDR. This result may be explained by the fact that the underlying presence of diabetic retinopathy may lead to more frequent fundus examinations. When we excluded severe comorbidities, including PDR at baseline, or when we analyzed events occurring >2 years after the index date, these associations were attenuated substantially or no longer statistically significant. It appears that reverse causality has worked.

The continuity of prescription for glucose-lowering drugs was found to be the most important indicator for the quality of diabetes care, as it was associated with the lowest risk of diabetes complications and all-cause mortality. This association remained regardless of regular outpatient visits. Adherence to glucose-lowering drugs reduced HbA_1c levels in all drug classes in a large U.K. primary care database (23). In meta-analysis, good medication adherence in type 2 diabetes decreased risk for hospitalization and all-cause mortality (24). Continuity of prescription for diabetes medication would be the key factor for reducing the risk of diabetes complications, independent of performing regular screening tests for complications.

Regardless of whether the quality assessment indicators were achieved, individuals managed in high-quality institutions were at a lower risk of developing diabetes complications and all-cause mortality. The quality of diabetes care depends both on the level of self-management of individuals with diabetes and the level of physician intervention. Physician factors such as attitudes, beliefs, and knowledge affect treatment efficacy and individuals’ self-management behaviors (9). Previous studies have demonstrated that diabetes management by physicians with a specialty in diabetes is associated with improved quality of diabetes care (25). These findings suggest the importance of delivery and access to high-quality care and regular consultations with physicians who specialize in diabetes for overall outcomes in individuals with diabetes.

Our study has several limitations. First, although we adjusted for various covariates, including treatment of disease and comorbidities, there is a possibility of residual confounders, such as laboratory tests, due to the limitation of claims data. Among the known indicators for measuring the quality of care (26), the current study only measured process-related indicators and could not measure the outcome-related indicators that assess the achievement of the target goals of the ABCs. Also, we did not include individual characteristics, such as socioeconomic status and health behaviors, which are well-known risk factors that affect the occurrence of diabetes complications. In Korea, the national health insurance services provide a database that includes household income and health behaviors such as smoking status, alcohol consumption, and physical activity, which are measured in the national health examinations. Therefore, further research to evaluate the comprehensive effect of individual behaviors and physician management on the prevention of diabetes complications is needed.

Second, we did not consider information on the duration and severity of diabetes. Instead, we assessed diabetes severity using insulin and the presence of diabetes-related complications.

Third, the NDQAP has been implemented only in primary care settings. In Korea, ∼30% of individuals with diabetes are treated at general or tertiary hospitals that are not included in the NDQAP (27). Thus, it is necessary to evaluate the risk of the development of diabetes complications based on the quality of diabetes care in general or tertiary hospitals.

Fourth, although the NDQAP included both type 1 and type 2 diabetes, and the same quality assessment indicators were applied, the prevalence of type 1 diabetes was only ∼0.05% in Korea (28). In addition, most individuals with type 1 diabetes are managed in general or tertiary hospitals. Therefore, our results can only be attributed to individuals with type 2 diabetes.

Finally, the quality assessment indicators were only measured at baseline in the main analysis. However, when considering changes in the quality assessment indicators after 2 years, approximately ≥70% of the participants did not any change in the achievement of quality assessment indicators. Furthermore, the overall pattern of association was similar to the main results after adjusting for the quality assessment indicators after 2 years.

In conclusion, the achievement of NDQAP indicators was associated with a decreased risk of diabetes complications and all-cause mortality. We found that adherence to quality assessment indicators may yield greater benefits for individuals with diabetes. This suggests that national-level quality care programs for diabetes management may be effective in improving health outcomes for individuals with diabetes. Therefore, policy efforts to encourage standardized and comprehensive diabetes management in primary care may be necessary.

Funding. This study was supported by the Joint Project on Quality Assessment Research of the Health Insurance Review and Assessment Service, Republic of Korea. This study used the Health Insurance Review and Assessment Service data (No. M20220127796) made by the Health Insurance Review and Assessment Service.

Duality of Interest. No potential conflicts of interest relevant to this article were reported.

Author Contributions. J.H.H. and K.H.H. wrote the first draft of the manuscript. K.H.H. and D.J.K. edited and reviewed the manuscript and interpreted the results. K.H.H. conducted the statistical analysis. S.K., G.O.K., B.Y.K., K.H.H., and D.J.K. were involved in the conception and design of the study. All authors approved the final version of the manuscript. K.H.H. and D.J.K. are the guarantors of this work and, as such, had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.