The positive predictive value of ankle fracture diagnosis in the Danish National Patient Registry

INTRODUCTION. Information on data validity is essential for understanding the precision of studies based on data from the Danish National Patient Registry (DNPR). Thus, the aim of this study was to validate the quality of ankle fracture data in the DNPR. METHODS. We identified all patients from four hospitals with a surgically treated ankle fracture between 1 January 2018 and 31 December 2018. The positive predictive value (PPV) was estimated for a random sample of 10% of patients with both a relevant ankle fracture diagnosis code and a relevant procedure code, as well as for patients with only a relevant ankle fracture diagnosis code or a relevant ankle fracture procedure code. We collected data from medical records and X-rays. Two consultants independently validated the ankle fracture diagnosis and procedure codes reported to the DNPR. RESULTS. Among the four centres, 651 patients were identified with both an ankle fracture diagnosis and a procedure code. Among these, data from 65 (10%) patients were extracted for validation. For these patients, the PPV for an ankle fracture was 0.95 (95% confidence interval (CI): 0.88-0.99). The PPV for the diagnosis code was 0.89 (95% CI: 0.79-0.95), and for the procedure code, the PPV was 0.82 (95% CI: 0.70-0.90). For patients with only an ankle fracture diagnosis code or only a surgical procedure code, the PPV for an ankle fracture was 0.77 (95% CI: 0.64-0.87). CONCLUSION. This study showed that ankle fracture diagnosis and procedure codes registered in the DNPR are of a high quality and thus constitute a valuable data source for research on ankle fractures.