Validation of an ICD-9-based claims algorithm for identifying patients with chronic idiopathic/spontaneous urticaria.

Background: There is no specific International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) code for chronic idiopathic urticaria or spontaneous urticaria (CIU/CSU), a skin condition characterized by hives and angioedema lasting at least 6 weeks with no known cause.

Objective: To validate an ICD-9-CM-based algorithm for identification of patients with CIU/CSU and thus facilitate claims-based research.

Methods: Patient records were reviewed at 4 US practices.