Reliability of Acute Pancreatitis Diagnosis Coding in a National Patient Register: A Validation Study in Sweden

Aim: National patient registers are powerful tools in epidemiological research and healthcare administration. As the level of reliability of diagnoses that are partly based on clinical signs, such as acute pancreatitis, may be low, the reliability of discharge diagnoses in these registers needs to be validated. The main aim of this study was to validate the diagnosis coding for acute pancreatitis in the Swedish National Patient Register. Method: We randomly sampled 650 admissions of all patients registered in the Swedish National Patient Register with acute pancreatitis or other nonmalignant pancreatic disorders as the main diagnosis in 2007 and 1998, and as the secondary diagnosis in 2007. The medical records for these admissions were reviewed. We analyzed the concordance between the coding of acute pancreatitis in the Swedish National Patient Register and criteria based on internationally accepted diagnostic standards. Results: We received 603 medical records for manual review. Among the 530 patients with a diagnosis of acute pancreatitis in the Swedish National Patient Register, 442 (83%) were, after review, defined as definitive acute pancreatitis, 80 (15%) as probable acute pancreatitis, and 8 (2%) as no acute pancreatitis. There were no significant differences in the reliability of the diagnosis with regard to sex, age, time period or whether the patient had been treated at a county or university hospital. Among the 73 patients registered with a non-malignant pancreatic disorder other than acute pancreatitis, the number of false-negative cases of acute pancreatitis was 23 (32%). They were mainly found among patients registered with a diagnosis of chronic pancreatitis. Conclusion: The Swedish National Patient Register is highly reliable as regards correct coding of acute pancreatitis. However, there seems to be a non-negligible share of false-negative cases of acute pancreatitis among patients registered with a diagnosis of chronic pancreatitis.