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Yuelian Sun,1– 4 Jesper Padkær Petersen,5 Chunsen Wu,6,7 Julie Werenberg Dreier,3,8 Rikke Damkjær Maimburg,9– 11 Tine Brink Henriksen,5 Jakob Christensen1,2 1Department of Neurology, Aarhus University Hospital, Aarhus, Denmark; 2Department of Clinical Medicine, Aarhus University, Aarhus, Denmark; 3National Centre for Register-Based Research, Aarhus University, Aarhus, Denmark; 4Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus University, Aarhus, Denmark; 5Department of Paediatrics, Clinical Institute, Aarhus University, Aarhus University Hospital, Aarhus, Denmark; 6Department of Clinical Research, University of Southern Denmark, Odense, Denmark; 7Department of Gynaecology and Obstetrics, Odense University Hospital, Odense, Denmark; 8Centre for Integrated Register-Based Research (CIRRAU), Aarhus University, Aarhus, Denmark; 9Department of Clinical Medicine, Aarhus University, Denmark; Department of Occupational Health, Aarhus University Hospital, Aarhus, Denmark; 10Department of Midwifery, University College of Northern Denmark, Hjørring, Denmark; 11School of Nursing and Midwifery, Western Sydney University, Blacktown, NSW, AustraliaCorrespondence: Yuelian Sun, Department of Neurology, Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark, Email ys@clin.au.dkPurpose: Phototherapy is the standard treatment for neonatal hyperbilirubinemia. It is important to collect data on phototherapy to support research related to the efficacy and safety of phototherapy. We explored the registration of phototherapy in the Danish National Patient Registry (DNPR) and the clinical characteristics of neonates treated with phototherapy.Methods: We identified children born alive in Denmark from 1 January 2000 through 30 November 2016 from the DNPR (N=1,044,502). We calculated the proportion of children registered that received phototherapy during the neonatal period and examined temporal trends, both nationwide and at the level of individual hospitals. In a sub-cohort of children born at Aarhus University Hospital (AUH) in 2002– 2016 (N=71,781), we analyzed the proportions of children registered that received phototherapy, according to sex, gestational age, birth weight, and neonatal characteristics, like Apgar score, birth asphyxia, and infections.Results: We identified 11,295 (1.1%) registered that received phototherapy. The proportions of children registered that received phototherapy differed among hospitals (range: 0 to 4.1%). Nationwide registration was low during the study period, but it increased to 1.8% in 2016. For the AUH sub-cohort the proportion of children registered with phototherapy averaged 4.4% (N=3182, range:3.9– 5.1%). The proportion of children registered with phototherapy was inversely correlated with gestational age and birth weight, and positively correlated with neonatal characteristics, including low Apgar score, birth asphyxia, and infections.Conclusion: Phototherapy was under-reported in the DNPR and the proportions of children registered that received phototherapy differed among hospitals. The non-compulsory policy for reporting treatment and care in hospitals to the DNPR might explain the variation. The most consistent reporting was observed among children born in an university hospital, where 4.4% of children registered that received phototherapy, and phototherapy was inversely associated with gestational age, birth weight, and positively associated with clinical characteristics like birth asphyxia, and infections.Keywords: Danish National Patient Registry, health administrative data, neonates, hyperbilirubinemia, neonatal jaundice, phototherapy

Yuelian Sun,1– 4 Julie Werenberg Dreier,3,5 Chunsen Wu,6,7 Vera Ehrenstein,4 Jakob Christensen2– 4 1Department of Clinical Medicine, Aarhus University, Aarhus, Denmark; 2Department of Neurology, Aarhus University Hospital, Aarhus, Denmark; 3National Centre for Register-Based Research, Department of Economics and Business Economics, Aarhus University, Aarhus, Denmark; 4Department of Clinical Epidemiology, Department of Clinical Medicine, Aarhus University Hospital, Aarhus, Denmark; 5Centre for Integrated Register-based Research (CIRRAU), Aarhus University, Aarhus, Denmark; 6Department of Clinical Research, University of Southern Denmark, Odense, Denmark; 7Department of Gynaecology and Obstetrics, Odense University Hospital, Odense, DenmarkCorrespondence: Yuelian Sun, Department of Clinical Medicine, Aarhus University, Aarhus, Denmark, Email ys@clin.au.dkObjective: The Danish National Patient Registry (DNPR) is a valuable resource for medical and epidemiological Research. However, not all research articles fully described procedures they used to identify events. In this study, we compared two approaches in identifying persons with a disease diagnosis using neonatal jaundice and epilepsy as examples.Methods: A cohort of singletons born alive between the 1st January 1997 and the 30th November 2016 in Denmark was used for this purpose. Diagnostic information for a hospital contact in the registry included a primary diagnosis, secondary diagnoses, referral diagnoses, and additional information to a diagnosis (associated diagnoses), if any. Approach 1 identified patients of interest by considering all diagnostic information with exclusion of referral diagnoses only. Approach 2 identified patients of interest by additionally excluding diagnoses from a hospital contact that were coded with Z00 – Z99 of ICD-10 (for health service on examination and reproduction, etc.) as the main reason of the hospital contact. We presented the proportion of people with a diagnosis of neonatal jaundice and epilepsy by the two approaches and explored the potential explanations for the difference.Results: For the example of neonatal jaundice, the study population included N=1,186,683 persons. The proportion of children with a diagnosis of neonatal jaundice was 5.5% (n=66,736) by approach 1 and 3.9% (n=45,928) by approach 2. For the example of epilepsy, the study population included N=1,183,273 persons. The proportion of children with a diagnosis of epilepsy were 1.2% (n=14,604) by approach 1 and 0.9% (n=10,441) by approach 2.Discussion: This study demonstrated that the two approaches identified different proportion of persons with a diagnosis of neonatal jaundice and epilepsy. We advocated researchers report complete procedures of identifying patients for making research findings reproducible and comparable.Keywords: the Danish National Patient Registry, health administrative data, misclassification of diagnosis