The incidence of hip fractures in Norway -accuracy of the national Norwegian patient registry

Background: Hip fractures incur the greatest medical costs of any fracture. Valid epidemiological data are important to monitor for time-dependent changes. In Norway, hip fractures are registered in the Norwegian Patient Registry (NPR), but no published national validation exists. The aim of the present study was a national validation of NPR as a register for hip fractures using diagnostic codes (ICD-10 S 72.0-2) and/or procedure codes (NOMESCO version 1.14 NFBxy (x = 0-9, y = 0-2) or NFJxy (x = 0-9, y = 0-2). Method: A nationwide, population-based cohort comprising a random sub-sample of 1,000 hip fracture-related entries for the years 2008-09 was drawn from the NPR. 200 entries were defined by a combination of diagnostic and procedure codes (subsample 1), 400 entries were defined by diagnostic codes only (subsample 2) and 400 entries were defined by procedure codes only (subsample 3). Accuracy was ascertained through comparison with discharge summaries, procedure notes and X-ray reports requested from 40 health institutions. Comparisons between groups were done by chi(2) for categorical and t-test for continuous variables. Results: 792 health records from 32 institutions were reviewed. High accuracy (98.2%, 95% C.I. 96.5-99.9%) was found for subsample 1, a combination of diagnostic and procedure codes. Coding errors were prominent in other subsamples. Defining fractures by a combination of diagnostic and procedure codes, annual average hip fracture incidence in Norway was 9,092 (95% C.I. 8,934-9,249), excluding only 6.5% of all hip fractures defined by wider definitions. Conclusions: Based on current coding practice in Norway, a reliable national estimate of hip fracture incidences is found by a combination of relevant ICD-10 and NOMESCO codes in the NPR. This method may be used for monitoring epidemiological changes.