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Abstract
Objective The German Diabetes Risk Score (GDRS) is a diabetes prediction model which only includes non-invasively measured risk factors. The aim of this study was to extend the original GDRS by hemoglobin A1c (HbA1c) and validate this clinical GDRS in the nationwide German National Health Interview and Examination Survey 1998 (GNHIES98) cohort.
Research design and methods Extension of the GDRS was based on the European Prospective Investigation into Cancer and Nutrition (EPIC)-Potsdam study with baseline assessment conducted between 1994 and 1998 (N=27 548, main age range 35–65 years). Cox regression was applied with the original GDRS and HbA1c as independent variables. The extended model was evaluated by discrimination (C-index (95% CI)), calibration (calibration plots and expected to observed (E:O) ratios (95% CI)), and reclassification (net reclassification improvement, NRI (95% CI)). For validation, data from the GNHIES98 cohort with baseline assessment conducted between 1997 and 1999 were used (N=3717, age range 18–79 years). Missing data were handled with multiple imputation.
Results After 5 years of follow-up 593 incident cases of type 2 diabetes occurred in EPIC-Potsdam and 86 in the GNHIES98 cohort. In EPIC-Potsdam, the C-index for the clinical GDRS was 0.87 (0.81 to 0.92) and the overall NRI was 0.26 (0.21 to 0.30), with a stronger improvement among cases compared with non-cases (NRIcases: 0.24 (0.19 to 0.28); NRInon-cases: 0.02 (0.01 to 0.02)). Almost perfect calibration was observed with a slight tendency toward overestimation, which was also reflected by an E:O ratio of 1.07 (0.99 to 1.16). In the GNHIES98 cohort, discrimination was excellent with a C-index of 0.91 (0.88 to 0.94). After recalibration, the calibration plot showed underestimation of diabetes risk in the highest risk group, while the E:O ratio indicated overall perfect calibration (1.02 (0.83 to 1.26)).
Conclusions The clinical GDRS provides the opportunity to apply the original GDRS as a first step in risk assessment, which can then be extended in clinical practice with HbA1c whenever it was measured.
- risk assessment
- clinical practice
- type 2 diabetes
- HbA1c
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Footnotes
KMüh and RP are joint first authors.
CH and MBS are joint last authors.
Presented at Workshop of the German Society of Epidemiology (DGEpi) “Prädiktionsmodelle für kardiometabolische Erkrankungen unter besonderer Berücksichtigung von Ernährungs- und Lebensstilfaktoren”: preliminary results in an invited presentation (28.11.2016, Berlin).
Contributors MBS and CH conceptualized the study. KM and RP defined the analytical strategy, analyzed the data and wrote the manuscript. HB was responsible for data collection of the EPIC-Potsdam study. H-GJ, MBS and CH contributed to the interpretation of the data and critically revised the manuscript. All authors approved the final version of the manuscript.
Funding This work was supported in part by a grant from the German Federal Ministry of Education and Research (BMBF) to the German Center for Diabetes Research (DZD e.V.). The recruitment phase of the EPIC-Potsdam Study was supported by the Federal Ministry of Science, Germany (01 EA 9401) and the European Union (SOC 95201408 05F02). The follow-up of the EPIC-Potsdam Study was supported by German Cancer Aid (70-2488-Ha I) and the European Community (SOC 98200769 05F02). Both GNHIES98 and DEGS1 were funded by the German Federal Ministry of Health.
Competing interests None declared.
Patient consent Not required.
Ethics approval Ethical Committee of the State of Brandenburg (EPIC-Potsdam) and Charité-Universitätsmedizin Berlin (GNHIES98 cohort).
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement In accordance with the German Federal and State data protection regulations, epidemiologic data analyses of EPIC-Potsdam may be conducted upon application addressed to HB (boeing@dife.de). Each application will have to pass a review process by a scientific board. The data set of the GNHIES98 cannot be made publicly available because informed consent from study participants did not cover public deposition of data. However, the minimal data set underlying the findings regarding the validation of the clinical GDRS presented in this study is archived in the ‘Health Monitoring’ Research Data Centre at the Robert Koch Institute (RKI) and can be accessed by all interested researchers. On-site access to the data set is possible at the Secure Data Center of the RKI’s ‘Health Monitoring’ Research Data Centre. Requests should be submitted to fdz@rki.de.