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

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          Abstract

          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.

          Objectives

          To review the content, data quality, and research potential of the DNPR.

          Methods

          We examined the setting, history, aims, content, and classification systems of the DNPR. We searched PubMed and the Danish Medical Journal to create a bibliography of validation studies. We included also studies that were referenced in retrieved papers or known to us beforehand. Methodological considerations related to DNPR data were reviewed.

          Results

          During 1977–2012, the DNPR registered 8,085,603 persons, accounting for 7,268,857 inpatient, 5,953,405 outpatient, and 5,097,300 emergency department contacts. The DNPR provides nationwide longitudinal registration of detailed administrative and clinical data. It has recorded information on all patients discharged from Danish nonpsychiatric hospitals since 1977 and on psychiatric inpatients and emergency department and outpatient specialty clinic contacts since 1995. For each patient contact, one primary and optional secondary diagnoses are recorded according to the International Classification of Diseases. The DNPR provides a data source to identify diseases, examinations, certain in-hospital medical treatments, and surgical procedures. Long-term temporal trends in hospitalization and treatment rates can be studied. The positive predictive values of diseases and treatments vary widely (<15%–100%). The DNPR data are linkable at the patient level with data from other Danish administrative registries, clinical registries, randomized controlled trials, population surveys, and epidemiologic field studies – enabling researchers to reconstruct individual life and health trajectories for an entire population.

          Conclusion

          The DNPR is a valuable tool for epidemiological research. However, both its strengths and limitations must be considered when interpreting research results, and continuous validation of its clinical data is essential.

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          Most cited references179

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          Epidemiology. When an entire country is a cohort.

          L. Frank (2000)
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            Validity of Stroke Diagnoses in a National Register of Patients

            Background: Many registers containing routine medical information have been developed for research and surveillance purposes. In epidemiological research assessment of endpoints is often conducted via registers. In the present study we validated stroke and transient ischemic attack (TIA) diagnoses in the Danish National Register of Patients (DNRP). Methods: Subjects from a Danish cohort study, the Copenhagen City Heart Study (n = 19,698), were crosslinked with the DNRP. The following International Classification of Disease 10th revision codes were used to identify possible strokes and TIAs: I60–I69 and G45. Two independent raters reviewed all cases. Positive predictive values of stroke, TIA and stroke subtypes were estimated by dividing the confirmed cases by the total number of cases located in the DNRP. Interrater reliability was tested using ĸ statistics. Results: Of 236 possible cerebrovascular events, 1 in 6 stroke diagnoses did not meet study criteria. The majority of events in the DNRP were registered as unspecified stroke (I64), n = 105 (44%), of which two thirds were diagnosed as ischemic stroke events by the raters. Intracerebral hemorrhage and ischemic stroke had a positive predictive value from 74 to 97%, respectively. Conclusion: Our results show that the DNRP tends to overestimate the number of cerebrovascular events, while ischemic stroke is underestimated.
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              Thrombotic stroke and myocardial infarction with hormonal contraception.

              Although several studies have assessed the risk of venous thromboembolism with newer hormonal contraception, few have examined thrombotic stroke and myocardial infarction, and results have been conflicting. In this 15-year Danish historical cohort study, we followed nonpregnant women, 15 to 49 years old, with no history of cardiovascular disease or cancer. Data on use of hormonal contraception, clinical end points, and potential confounders were obtained from four national registries. A total of 1,626,158 women contributed 14,251,063 person-years of observation, during which 3311 thrombotic strokes (21.4 per 100,000 person-years) and 1725 myocardial infarctions (10.1 per 100,000 person-years) occurred. As compared with nonuse, current use of oral contraceptives that included ethinyl estradiol at a dose of 30 to 40 μg was associated with the following relative risks (and 95% confidence intervals) for thrombotic stroke and myocardial infarction, according to progestin type: norethindrone, 2.2 (1.5 to 3.2) and 2.3 (1.3 to 3.9); levonorgestrel, 1.7 (1.4 to 2.0) and 2.0 (1.6 to 2.5); norgestimate, 1.5 (1.2 to 1.9) and 1.3 (0.9 to 1.9); desogestrel, 2.2 (1.8 to 2.7) and 2.1 (1.5 to 2.8); gestodene, 1.8 (1.6 to 2.0) and 1.9 (1.6 to 2.3); and drospirenone, 1.6 (1.2 to 2.2) and 1.7 (1.0 to 2.6), respectively. With ethinyl estradiol at a dose of 20 μg, the corresponding relative risks according to progestin type were as follows: desogestrel, 1.5 (1.3 to 1.9) and 1.6 (1.1 to 2.1); gestodene, 1.7 (1.4 to 2.1) and 1.2 (0.8 to 1.9); and drospirenone, 0.9 (0.2 to 3.5) and 0.0. For transdermal patches, the corresponding relative risks were 3.2 (0.8 to 12.6) and 0.0, and for a vaginal ring, 2.5 (1.4 to 4.4) and 2.1 (0.7 to 6.5). Although the absolute risks of thrombotic stroke and myocardial infarction associated with the use of hormonal contraception were low, the risk was increased by a factor of 0.9 to 1.7 with oral contraceptives that included ethinyl estradiol at a dose of 20 μg and by a factor of 1.3 to 2.3 with those that included ethinyl estradiol at a dose of 30 to 40 μg, with relatively small differences in risk according to progestin type. (Funded by the Danish Heart Association.).
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                Author and article information

                Journal
                Clin Epidemiol
                Clin Epidemiol
                Clinical Epidemiology
                Clinical Epidemiology
                Dove Medical Press
                1179-1349
                2015
                17 November 2015
                : 7
                : 449-490
                Affiliations
                [1 ]Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark
                [2 ]Department of Health Documentation, State Serum Institute, Copenhagen, Denmark
                Author notes
                Correspondence: Morten Schmidt, Department of Clinical Epidemiology, Aarhus University Hospital, Olof Palmes Allé 43-45, 8200 Aarhus North, Denmark, Tel +45 8716 8063, Fax +45 8716 7215, Email morten.schmidt@ 123456clin.au.dk
                Article
                clep-7-449
                10.2147/CLEP.S91125
                4655913
                26604824
                df0b6673-edb7-42b6-95d9-2b36818277fd
                © 2015 Schmidt et al. This work is published by Dove Medical Press Limited, and licensed under Creative Commons Attribution – Non Commercial (unported, v3.0) License

                The full terms of the License are available at http://creativecommons.org/licenses/by-nc/3.0/. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed.

                History
                Categories
                Review

                Public health
                epidemiological methods,medical record linkage,registries,research design,validation studies

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