Discussion
Community-dwelling adults aged 45–79 years with type 2 diabetes in Germany showed consistent improvements in diabetes care between the survey periods 1997–1999 and 2008–2011. Improvement was seen for treatment targets (HbA1c, BP, serum lipids), statin and ACE inhibitor/ARB use. Self-monitoring of blood glucose levels and uptake of annual eye or foot examinations also improved. Furthermore, the proportion of adults with type 2 diabetes reporting any diabetes-specific complications and comorbid CVD decreased significantly. However, there was no significant decrease in the proportions of adults with diabetes having evidence of CKD. The proportion of people with diabetes and obesity rose over this period and the proportion of those currently smoking was unchanged. Although overall engagement in sports activity significantly improved over time, less than one in five adults in 2008–2011 reported performing more than 2 hours of sports activity per week; this is well below the guideline recommended levels of physical activity (>150 min/week) for adults with diabetes.3 ,6
There may be several reasons for the observed improvements in some, albeit not all, diabetes care indicators in Germany. First, there was the introduction of a national type 2 DMP in 2003, between these national health examination surveys 1997–1999 and 2008–2011.8 DMP enrollment comprises regular check-up visits and aims to promote diabetes education, adherence to treatment goals, and self-management.8 ,27 ,28 Physicians are contracted under the provision of structural quality requirements and reimbursement is provided with a focus on intermediate outcome measures, such as HbA1c measures. This key national policy change and the introduction of financial incentives for physicians to improve diabetes care are likely to have contributed to the improvements in glycemic control and statin use as observed in the present study. However, we found mixed results regarding diabetes self-management with improvements in glucose self-monitoring but not keeping a diabetes passport. Second, evidence-based national diabetes management and treatment guidelines have been periodically updated between the survey periods and are integral to DMP contracts.6 Third, guideline recommendations regarding the diagnostic criteria for type 2 diabetes based on fasting glucose changed in 1998, that is, toward the end of GNHIES98.29 Together, these changes in between survey periods might have contributed to an earlier diagnosis of type 2 diabetes. We found that the age at diagnosis of diabetes was on average 1.7 years earlier in DEGS1 than in GNHIES98. Survey participants detected at an earlier phase of the disease course may have more favorable intermediate outcome measures (HbA1c, BP, cholesterol), and are less likely to have diabetes-specific complications compared with those at a more advanced phase of disease. In sex-specific analyses, a significant difference regarding an earlier age at diagnosis in DEGS1 vs GNHIES98 was confined to women, which may reflect sex differences in care (eg, diagnosis of gestational diabetes) and/or healthcare services utilization.
In Germany, previous studies of changes in diabetes quality of care indicators over time have been confined to regional population-based studies11 or studies among primary care patients.30 In repeated population surveys conducted in southern Germany, recommended eye or foot examinations among adults with type 2 diabetes significantly increased between 1999–2001 and 2006–2008 (60.5% vs 71.3% and 37.5% vs 55.1% respectively), as did the use of lipid-lowering drugs (18.0% vs 37.9%), and the percentage of adults with diabetes achieving BP targets of <140/90 mm Hg (43.6% vs 70.5%).11 These findings are largely consistent with our results. However, unlike our findings, the proportions of persons with diabetes achieving HbA1c targets of <7.0% (53 mmol/mol) and those with a BMI ≤30 kg/m2 remained unchanged in the previous study.11 In a study based on data from 110 primary care practices across Germany, the proportion of patients with diabetes achieving HbA1c <6.5% (48 mmol/mol) increased from 31% in 1998 to 36% in 2005, while the percentage of patients with HbA1c ≥9.0% (75 mmol/mol) was halved from about 20% to 10% over this time period,30 roughly comparable to our findings from 23.5% in 1997–1999 to 4.6% in 2008–2011 (table 2). Our findings of improvements in diabetes-related complications among our sample are consistent with a variety of studies using various data sources over the past decade in Germany (eg, regional disease registries or hospital discharge data, selected sickness funds) reporting improvements in amputation rates, the incidence of blindness, and cardiovascular risk reduction, particularly among women.31–33
Time trend analyses of diabetes care indicators based on repeated national health surveys have been conducted in the USA. Results from these studies have consistently demonstrated significant improvements in the control of HbA1c, BP, and lipids among adults with diabetes, although absolute changes over the past decade were generally smaller than those observed in the present study.21 ,34–37 Between the 1999–2002 and 2007–2010 NHANES survey waves, the proportion of adults with diabetes achieving HbA1c <7.0% (53 mmol/mol), BP <130/80 mm Hg, and LDL-cholesterol <100 mg/dL increased significantly by 7.9, 11.7, and 20.8 percentage points, respectively,21 as compared to 32.9, 15.2, and 28.3 percentage points for HbA1c <7.0% (53 mmol/mol), BP <130/80 mm Hg, and TC <190 mg/dL in the present analysis. Unfortunately, some indicators are not directly comparable between NHANES and the German national health surveys. Unlike NHANES, the present study used TC instead of LDL-cholesterol, as the German surveys did not recruit a random subsample of adults who observed overnight fasting for at least 8 h.13 ,14 Alongside the significantly improved profiles of HbA1c, BP measures, and cholesterol, use of antidiabetic medication, antihypertensive agents, and lipid-lowering drugs significantly increased over time as observed in our study and previously in US population studies.34–37 We found that 8.0% of adults with diabetes in GNHIES98 and 13.6% in DEGS1 used a combination of insulin and oral agents, similar to 9.8% and 13.9% of adults with diabetes in the 1999–2004 and 2005–2010 NHANES waves.34 Over the same time period, lipid-lowering drug use increased from 18.2% to 39.6% among adults with diabetes in Germany as shown in this analysis, similar to increases in NHANES participants from 19.5% in 1999–2000 to 42.2% in 2007–2008.38 Consistent with our findings, analyses of data from the US Behavioral Risk Factor Surveillance System (BRFSS) survey waves 2000 and 2008 showed significant improvements with respect to the proportion of adults with diabetes reporting annual foot examinations and glucose self-monitoring.21 Unlike our findings, self-reported eye examination among adults with diabetes in BRFSS showed no further improvement over time,21 but baseline coverage for this indicator already achieved a much higher level in the USA in the 2000 survey with 75.1% compared to 51.1% in GNHIES98. Data from official health statistics (National Hospital Discharge Survey, US Renal Data System, National Vital Statistics System) have been systematically used to analyze trends in rates of diabetes-related complications in the USA and provide clear evidence for a decline in myocardial infarction, and death from hyperglycemic crisis, stroke, and amputation among people with diabetes between 1990 to 2010.39 This remains a major goal for diabetes surveillance in Germany, where evidence on long-term outcomes is limited so far.8
Despite significant improvements in diabetes care observed over the past decade, the current level of care in Germany as in other countries such as the USA,21 ,34–37 Canada,40 and Spain41 falls short of guideline recommendations. Similar to these studies,21 ,40 ,41 the results of the present analysis based on data from German national health surveys show that about two-thirds of persons with type 2 diabetes reached the target of HbA1c <7.0% (53 mmol/mol), and only 11.4% of patients with diabetes achieved stringent targets in HbA1c, TC, BP, and smoking combined. There was little change in the prevalence of current smokers among adults with diabetes in our study similar to US diabetes population studies.21 ,37 Rising obesity among diabetes populations is a concern for numerous countries37 and highlights population challenges of guideline-recommended weight reduction. Weight gain among persons with diabetes has been observed in relation to treatment with insulin and certain oral antidiabetic agents.42 ,43 Further insight from longitudinal studies is needed to assess the effect of weight gain on long-term cardiovascular risk and mortality.42 ,43
The major strength of this analysis is that it provides comprehensive data on changes in diabetes quality of care indicators over time including the time period before (1997–1999) and after (2008–2011) the introduction of DMPs and national evidence-based guideline implementation for type 2 diabetes in Germany. There are several limitations to this study. First, we cannot exclude selection bias, as persons who are severely ill, hospitalized, or institutionalized were not included. Therefore, our results may depict an overly optimistic picture of diabetes quality of care both cross-sectionally and over time. Second, diabetes diagnosis was self-reported and not verified by medical records as occurs in studies using patient registers. However, self-reported physician-diagnosed diabetes provides a valid and internationally established indicator7 ,34 ,44 which permits comparisons between countries as well as over time. Third, information on gestational diabetes was collected in DEGS17 but not in GNHIES98. Inclusion of women with gestational diabetes may have reduced the survey-specific rates of persons with diabetes who received pharmacological treatment or preventive eye and foot examinations in this study. Fourth, although data collection methods were kept comparable between surveys as far as possible, changes to analytical methods for physiological measurements remain a challenge to population-based monitoring of BP and biomarkers.18 ,34 Finally, this analysis was limited to intermediate outcome and process indicators of diabetes care available in both surveys. In particular, process of care indicators reflecting self-management and patient education were limited to glucose self-monitoring and holding a diabetes passport in this study.