Use of combined search criteria improved validity of rare disease (craniopharyngioma) diagnosis in a national registry

OBJECTIVE: To evaluate sensitivity and validity of the Danish National Patient Registry (NPR) including relevant International Classification of Diseases, Eighth Revision (ICD-8) and International Classification of Diseases, Tenth Revision (ICD-10) codes and explore potential benefits of combining diagnosis and department codes in composite search strategies. STUDY DESIGN AND SETTING: The study period was 1985-2004. Medical records of patients identified with one or more of seven ICD-8 or ICD-10 codes from a number of registries were reviewed to confirm or reject the craniopharyngioma diagnosis. NPR sensitivity was evaluated in North Jutland County through comparison with hospital registries, the county registry, and the Danish Cancer Registry. Codes and search strategies were studied using NPR data from Denmark (population 5.2 million). RESULTS: In the North Jutland County study, the NPR identified 95% of new patients with histologically verified or probable craniopharyngioma. In the code and search strategy studies, the NPR search identified 684 patients. Records were retrieved in 607 (89%), of whom 185 (30%) had verified or probable craniopharyngioma. Searches combining "best code" and "highly specialized department" or "neurosurgery procedure" registrations improved validity considerably, whereas reducing sensitivity only modestly. CONCLUSION: The NPR identified 95% of new craniopharyngioma patients, but only 30% of cases were correct. Validity was improved by applying a modified composite search strategy.