Bullous Pemphigoid: Validation of the National Patient Register in Two Counties in Sweden, 2001 to 2012

Bullous pemphigoid (BP) is the most common autoimmune blistering disease. Since 2001, data from all specialized outpatient and inpatient care institutions in Sweden, have been registered with the National Patient Register (NPR), based on a unique personal identification number. Previous validations of the register have shown high accuracy for various non-dermatological autoimmune diseases. In order to validate the diagnosis of BP, all residents aged < 20 years in 2 counties in Sweden (539,000 inhabitants) diagnosed with bullous pemphigoid (ICD-10; L12.0, L12.8, L12.9) in the period 2001 to 2012 were identified in the NPR. Medical records, as well as immuno- and histopathological data, were reviewed for this study. A total of 323 patients with BP were identified in the NPR. Of these, 178 patients had a directly confirmed diagnosis of BP from immuno- and histopathological data, reviewed by a dermatopathologist. For the remaining 145 patients medical records were retrieved and further reviewed by 2 dermatologists. Of these, 105 patients had a confirmed diagnosis of BP. The medical records of 16 patients were missing, and 24 patients were not classified as having BP. Overall, a positive predictive value of 92% (283/307) was found for BP in the NPR. In conclusion, the present validation of medical records and immuno- and histopathological data showed high validity for the diagnosis of BP in the Swedish NPR.