Incidence of Graves’ Disease with Validation and Completeness of the Diagnosis for Registry Extracts in the Danish National Patient Register

Frederik Østergaard Klit,1,2 Jakob Dal,1– 3 Stine Linding Andersen,1,4 Amar Nikontovic,3 Peter Vestergaard,2,3 Jesper Scott Karmisholt1,2 1Department of Clinical Medicine, Aalborg University, Aalborg, Denmark; 2Department of Endocrinology, Aalborg University Hospital, Aalborg, Denmark; 3Steno Diabetes Center North Denmark, Aalborg, Denmark; 4Department of Clinical Biochemistry, Aalborg University Hospital, Aalborg, DenmarkCorrespondence: Frederik Østergaard Klit, Email [email protected]: Graves’ disease (GD) is one of the most common causes of thyrotoxicosis. It has been proposed to identify incident GD by using the GD-specific code, E05.0, of the 10th revision of the International Classification of Disease (ICD-10) in the Danish National Patient Register (DNPR). We aimed to report the incidence of GD and to investigate the validity and completeness of E05.0 registration using Aalborg University Hospital (AaUH) as a single centre-sample.Patients and Methods: The study included registry data from 2020 to 2022. The study population (n=2,893) comprised all people (15– 99 years) in the catchment area of AaUH (n=244,872) with either positive anti-thyroid stimulating hormone receptor antibodies (TRAb), or registered with a thyroid disease related ICD-10 code E03.0-E07.9, O99.2 or O90.5 at the Department of Endocrinology, AaUH. To identify incident cases, all subjects occurring for the first time in 2020 were excluded (n=2,339). The incident subjects were categorized into a general practice (n=63) or hospital care group (n=491) and underwent GD verification by biochemical tests and thyroid imaging. Validity was evaluated by positive (PPV) and negative (NPV) predictive values and completeness of E05.0 registration was estimated to the total number of verified GD subjects in hospital care only and in overall (groups combined).Results: One hundred thirty-one incident GD subjects were identified corresponding to an incidence of 26.8 per 100,000/year. E05.0 had a PPV of 90% [95% CI: 81;96] and a NPV of 90% [95% CI: 85;93] to identify incident cases of GD. Completeness was estimated to be 73% [95% CI: 63;82] in hospital care and 50– 60% [95% CI: 41;68] in overall.Conclusion: We report on a similar incidence of GD as previous studies in Denmark. Despite a high PPV, incident cases of GD could not adequately be identified by E05.0 in DNPR due to low completeness. Researchers should rely on biochemical test results to identify incident GD.Keywords: E05.0, epidemiology, hyperthyroid disease, validation, ICD, DNPR