Original Article
The Danish National Hospital Register is a valuable study base for epidemiologic research in febrile seizures

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Abstract

Background and Objectives

We examined the quality and completeness of the discharge diagnosis of febrile seizures in the Danish National Hospital Register (DNHR).

Methods

We invited all children born at the Department of Obstetrics, Aarhus University Hospital, Denmark, between January 1990 and April 1992, to participate in the study. We collected information on febrile seizures in March 2001 by mailing a questionnaire to the mothers. Reported febrile seizures were verified by telephone interviews or review of medical records. We linked the cohort to the DNHR by means of a unique civil registry number assigned to all Danish citizens at birth. Overall, 6,624 (73%) children participated in the study.

Results

We found that 323 (4.9%) children in the cohort had had febrile seizures, and 231 of those were registered in the DNHR (completeness: 71.5%, 95% CI: 66.3–76.4). Furthermore, we confirmed the diagnosis in 231 of 249 children registered with febrile seizures in the DNHR (predictive value of a positive registration: 92.8%, 95% CI: 88.8–95.7).

Conclusion

The Danish National Hospital Register is a valuable tool for epidemiologic research in febrile seizures.

Introduction

Febrile seizures are the most common type of seizures in childhood, affecting 2–5% of all children [1], [2]. The etiology remains unknown, but depends most likely on interactions between genetic and environmental factors [3]. Observational studies suggest that febrile seizures are benign for the vast majority of children [4], [5], [6]. However, no studies have had a sufficient sample size or follow-up time to study long-term prognosis [7], and mounting evidence from neuroimaging studies and experiments in animals suggest that prolonged febrile seizures may cause brain damage in some individuals [8], [9], [10]. Thus, large population-based cohort studies with long-term follow-up are needed to study the aetiology and outcome of this common condition. However, these studies are often difficult to conduct due to high expenses and low participation rates. Secondary data such as hospital discharge registers and data bases may constitute a valuable and cost-efficient alternative to using primary data [11]. However, the quality and completeness of the data play an important role when designing studies and interpreting results.

We aimed at evaluating the data quality of the febrile seizures discharge diagnose in the Danish National Hospital Register (DNHR) for participants in the Aarhus Birth Cohort by comparing it with a reference standard based on information from questionnaires, telephone interviews, and medical records.

Section snippets

The Aarhus Birth Cohort

We invited all children who were born at the Department of Gynecology and Obstetrics, Aarhus University Hospital, Denmark, by Danish women between January 1990 and April 1992, to participate in the study, given that the child and the mother were alive in March 2001 (N = 9.058). The department is the only maternity ward in Aarhus serving a population of approximately 250,000 individuals.

We mailed a self-administrated questionnaire to the mothers in the study in March 2001. The questionnaire

Results

Among the 6,624 children who participated in the Aarhus Birth Cohort, 437 (6.6%) had experienced febrile seizures according to the parental questionnaire and 249 (3.8%) were registered with febrile seizures in the Danish National Hospital Register.

Overall, 247 children were registered with febrile seizures in both the DNHR and the parental questionnaire, 190 children had febrile seizures according to the questionnaire but not according to the DNHR, and two children were registered with febrile

Discussion

We evaluated the data quality of a febrile seizure diagnose in the DNHR by using information from a population-based cohort study of 6,624 children. We found that the predictive value of a positive registration of febrile seizures in the DNHR was high (∼93%), and that approximately three out of four children with a history of febrile seizures in the cohort were registered in the register. The completeness of the register increased with increasing duration of the febrile seizures, and children

Acknowledgments

This study was supported by grants from the Danish Medical Research Council, Ronald McDonald House Charities, and Danish Epilepsy Society. The activities of the Danish Epidemiology Science Centre are financed by a grant from the Danish National Research Foundation.

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