[An updated review of The Swedish National Patient Register as a data source].

The Swedish National Patient Register (NPR) is vital for epidemiological research. A 2010 review assessed the validity of inpatient diagnoses, but outpatient data were excluded. A recent review in the European Journal of Epidemiology examined validation studies for inpatient diagnoses post-2010 and outpatient data since 2001. Across 89 publications, median positive predictive value (PPV) was 84% for diagnoses (range: 18-100%) and 97% for surgical codes. Sensitivity was lower, median 73% (range: 45-80%). PPV and sensitivity varied depending on diagnosis, coding, reference standard, and data source. Different diagnostic criteria are needed depending on research question. Combining NPR with other registers can enhance accuracy. Limitations include incomplete outpatient data in early years, gaps in private healthcare reporting, and insufficient coverage of certain medical codes. Despite this, the NPR remains a reliable and central data source for medical research when limitations are considered.