Data Resource Profile: The Danish National Prescription Registry Anton Pottegård,* Sigrun Alba Johannesdottir Schmidt, Helle Wallach-Kildemoes, Henrik Toft Sørensen, Jesper Hallas and Morten Schmidt Clinical Pharmacology and Pharmacy, University of Southern Denmark, Odense, Denmark, Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark, Social and Clinical Pharmacy, University of Copenhagen, Copenhagen, Denmark and Department of Internal Medicine, Regional Hospital of Randers, Randers, Denmark

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Data Resource Profile: The Danish National Prescription Registry.

Denmark has a large network of population-based medical databases, which routinely collect high-quality data as a by-product of health care provision. The Danish medical databases include administrative, health, and clinical quality databases. Understanding the full research potential of these data sources requires insight into the underlying health care system. This review describes key elements of the Danish health care system from planning and delivery to record generation. First, it presents the history of the health care system, its overall organization and financing. Second, it details delivery of primary, hospital, psychiatric, and elderly care. Third, the path from a health care contact to a database record is followed. Finally, an overview of the available data sources is presented. This review discusses the data quality of each type of medical database and describes the relative technical ease and cost-effectiveness of exact individual-level linkage among them. It is shown, from an epidemiological point of view, how Denmark's population represents an open dynamic cohort with complete long-term follow-up, censored only at emigration or death. It is concluded that Denmark's constellation of universal health care, long-standing routine registration of most health and life events, and the possibility of exact individual-level data linkage provides unlimited possibilities for epidemiological research.

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The Danish health care system and epidemiological research: from health care contacts to database records

Objective The majority of cardiovascular diagnoses in the Danish National Patient Registry (DNPR) remain to be validated despite extensive use in epidemiological research. We therefore examined the positive predictive value (PPV) of cardiovascular diagnoses in the DNPR. Design Population-based validation study. Setting 1 university hospital and 2 regional hospitals in the Central Denmark Region, 2010–2012. Participants For each cardiovascular diagnosis, up to 100 patients from participating hospitals were randomly sampled during the study period using the DNPR. Main outcome measure Using medical record review as the reference standard, we examined the PPV for cardiovascular diagnoses in the DNPR, coded according to the International Classification of Diseases, 10th Revision. Results A total of 2153 medical records (97% of the total sample) were available for review. The PPVs ranged from 64% to 100%, with a mean PPV of 88%. The PPVs were ≥90% for first-time myocardial infarction, stent thrombosis, stable angina pectoris, hypertrophic cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, takotsubo cardiomyopathy, arterial hypertension, atrial fibrillation or flutter, cardiac arrest, mitral valve regurgitation or stenosis, aortic valve regurgitation or stenosis, pericarditis, hypercholesterolaemia, aortic dissection, aortic aneurysm/dilation and arterial claudication. The PPVs were between 80% and 90% for recurrent myocardial infarction, first-time unstable angina pectoris, pulmonary hypertension, bradycardia, ventricular tachycardia/fibrillation, endocarditis, cardiac tumours, first-time venous thromboembolism and between 70% and 80% for first-time and recurrent admission due to heart failure, first-time dilated cardiomyopathy, restrictive cardiomyopathy and recurrent venous thromboembolism. The PPV for first-time myocarditis was 64%. The PPVs were consistent within age, sex, calendar year and hospital categories. Conclusions The validity of cardiovascular diagnoses in the DNPR is overall high and sufficient for use in research since 2010.

https://bmjopen.bmj.com/content/bmjopen/6/11/e012832.full.pdf

Positive predictive value of cardiovascular diagnoses in the Danish National Patient Registry: a validation study.

The Danish Medical Birth Register was established in 1973. It is a key component of the Danish health information system. The register enables monitoring of the health of pregnant women and their offspring, it provides data for quality assessment of the perinatal care in Denmark, and it is used extensively for research. The register underwent major changes in construction and content in 1997, and new variables have been added during the last 20 years. The aim was to provide an updated description of the register focusing on structure, content, and coverage since 1997. The register includes data on all births in Denmark and comprises primarily of data from the Danish National Patient Registry supplemented with forms on home deliveries and stillbirths. It contains information on maternal age provided by the Civil Registration System. Information on pre-pregnancy body mass index and smoking in first trimester is collected in early pregnancy (first antenatal visit). The individual-level data can be linked to other Danish health registers such as the National Patient Registry and the Danish National Prescription Registry. The register informs several other registers/databases such as the Danish Twin Registry and the Danish Fetal Medicine Database. Aggregated data can be publicly accessed on the Danish Health Data Authority web page (
 www.esundhed.dk/sundhedsregistre/MFR
 ). Researchers can obtain access to individual-level pseudo-anonymised data via servers at Statistics Denmark and the Danish Health Data Authority.

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The Danish Medical Birth Register.

Aims: The Finnish Hospital Discharge Register (FHDR) is one of the oldest individual level hospital discharge registers and has been intensively used for research purposes. The aim of this study was to gather information concerning the quality of FHDR into one place in terms of a systematic review of validation studies that compare data to external information. Methods: Several reference databases were searched for validity articles published until January 2012. For each included study, focus of validation, register years examined, number of compared observations, external source(s) of data, summary of validation results, and conclusions concerning the validity of FHDR were extracted. Results: In total, 32 different studies comparing FHDR data to external information were identified. Most of the studies examined validity in the case of vascular disease, mental disorders or injuries. More than 95% of discharges could be identified from the register. Positive predictive value (PPV) for common diagnoses was ...

Quality of the Finnish Hospital Discharge Register: A systematic review

Background
The Danish National Patient Registry (DNPR) is one of the world’s oldest nationwide hospital registries and is used extensively for research. Many studies have validated algorithms for identifying health events in the DNPR, but the reports are fragmented and no overview exists.

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Jakob Lynge Sandegaard

Papers

The Danish National Patient Registry: a review of content, data quality, and research potential.