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Objectives and questions: The increasing prevalence of diabetes mellitus and its associated healthcare costs pose a significant economic burden on Germany, which continues to grow. The German Diagnosis-Related Group (G-DRG) system has been in place since 2004 to improve efficiency, ensure sustainability, and promote risk-sharing between healthcare providers and payers. This system determines DRG groups based on inpatient clinical characteristics and discharge coding. However, inadequate or inaccurate coding of diabetes mellitus as a secondary diagnosis can have negative clinical and financial consequences for healthcare systems. This study aims to assess the impact of coding diabetes mellitus as a secondary diagnosis within the current G-DRG system at a Level 1 Trauma Center.

Methods: This study includes all inpatient §21 data records (INEK) from a Level 1 Trauma Center between 2019 and 2023. Diabetes-related secondary diagnoses were identified using ICD-10 codes (E10-E14, O24, and R73). DRG regrouping and reimbursement calculations were performed using the ID EFIX software, version 11.0.0. Retrospective extraction of blood values and anamnesis reports was conducted through the hospital’s MEDICO system.

Results: A total of 49,313 inpatient cases were analyzed, including 108 diabetes-related ICD-10 codes. The proportion of patients coded for being diabetics was 7.65%, 5.97%, 7.07%, 6.82%, and 8.21%, in 2019, 2020, 2021, 2022, and 2023, respectively. By checking HbA1C values available for only 3.91%, 3.82%, 17.33%, 4.76%, and 6.98% of the cases for the respective years, the proportion of patients identified as having diabetes mellitus increased to 10.55%, 9.73%, 10.84%, 10.83%, and 11.80%, respectively.

Additionally, the simulation analyses using the 108 diabetes-related ICD-10 codes revealed that 95 codes had sufficient impact on DRG assignment, while 13 codes had minimal or no influence. Based on these simulations, proper coding could potentially generate a maximum reimbursement of € 38,740.15 per case, totaling a maximum of € 2,573,020.27 annually for the healthcare provider.

Discussion and conclusions: This retrospective analysis highlights a significant gap in the proper coding of diabetes mellitus in the hospital system, with more than 30% of diabetic patients not being documented correctly. The relatively low frequency of HbA1c testing further suggests that many diabetic patients may be overlooked. Identifying and documenting diabetes mellitus correctly is not only crucial for patient care and clinical outcomes but also plays a vital role in optimizing financial reimbursement. Accurate documentation and coding practices are essential for strengthening the healthcare system and ensuring balanced risk-sharing between providers and payers under the G-DRG system.