Positive predictive value of ICD-10 diagnosis codes for brain abscess in the Danish National Patient Registry

Purpose: To evaluate the positive predictive value (PPV) of ICD-10 diagnosis codes for brain abscess in the Danish National Patient Registry (DNPR). Patients and methods: We examined medical records of all patients with a first-time diagnosis code of brain abscess in the DNPR from 2007 to 2016. Patients were categorized with either confirmed or disproved brain abscess using a priori defined criteria. We computed the PPV as the proportion of confirmed diagnoses. Results: We identified 709 patients, of whom the medical records could not be retrieved for 15 patients, leaving 694 for further analyses. Of these, 444 had a confirmed brain abscess and 250 had another proven diagnosis, including 47 cases of intracranial empyema. The overall PPV was 64% (95% CI: 60-68) ranging from 24% to 96% among the different codes evaluated. By including only patients with either 1) both a diagnosis and surgical procedure code for brain abscess or 2) patients admitted to hospital with certain primary diagnosis codes (DG060[C,E,F] or DG079B) without newly diagnosed central nervous system (CNS) cancer, spondylodiscitis/intraspinal abscess, or procedure codes for evacuation of intracranial empyema, the PPV increased to 84% (95% CI 80-87) and 89% (395/444) of all confirmed cases were identified. Conclusion: The overall PPV of diagnosis codes for brain abscess in the DNPR was moderate. However, by exclusion of newly diagnosed CNS tumors, spondylodiscitis/intraspinal abscess, and intracranial empyemas, the PPV was high and therefore suitable for future registry-based studies of brain abscess.