The validity of the schizophrenia diagnosis in the Danish Psychiatric Central Research Register is good.

INTRODUCTION The Danish Psychiatric Central Research Register (DPCRR) has been used extensively for research purposes during the past decades. The aim of this study was to investigate the validity of the International Classification of Diseases (ICD)-10 schizophrenia diagnosis in the DPCRR. MATERIAL AND METHODS A random sample of 300 patients with a first-time diagnosis of schizophrenia (ICD-10 codes F20.0-F20.3 and F20.9) in 2009 was drawn from the register to assess its validity. The case records were reviewed by a Schedules for Clinical Assessment in Neuropsychiatry-certified psychiatric resident using the ICD-10 diagnostic criteria as reference. RESULTS The sample of 300 patients with schizophrenia represented 23.3% of all incident cases (n = 1,288) registered in 2009. We obtained 291 (97.0%) of the case records (nine were lost or inaccessible). Two case records (0.7%) were excluded because of foreign citizenship as these patients had prior episodes in other countries. Thirteen cases (4.3%) were erroneously registered as schizophrenia in the DPCRR. Of the remaining 276 patients, 269 (97.5%) fulfilled the ICD-10 diagnostic criteria for schizophrenia. In a worst case model including all 300 case records, the validity of the schizophrenia diagnosis was 89.7%. CONCLUSION According to this assessment of patient case records, the diagnosis of schizophrenia in the DPCRR has a high validity and is well-suited for research. FUNDING Aalborg Psychiatric Hospital funded the study, but the institution had no influence on the planning of the study or the preparation of the manuscript. TRIAL REGISTRATION not relevant.