Importance of Reporting Complete Procedures of Identifying Patients from the Danish National Patient Registry: The Case of Neonatal Jaundice and Epilepsy.

Objective: 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.