Positive predictive value of the ICD-10 hospital diagnosis of pleural empyema in the Danish National Registry of Patients

OBJECTIVE Health care databases are a valuable source for epidemiological research in respiratory diseases if diagnoses are valid. We validated the International Classification of Diseases, 10th revision (ICD-10) diagnosis of pleural empyema in the Danish National Registry of Patients (DNRP). METHODS We randomly selected hospitalized patients registered in the DNRP with a discharge diagnosis of pleural empyema between 1995 and 2009 in the North Denmark Region. We retrieved and reviewed medical records and estimated the positive predictive value (PPV) of the empyema diagnosis. Analyses were stratified by study period, hospital type (referral versus district), department type (pulmonary medicine or thoracic surgery versus other), cause of empyema (medical, surgical, or traumatic), and age group. To assess changes over time, we included chi-square tests for linear trend. RESULTS We retrieved the medical records of 224/225 sampled patients with empyema (99.6%). Of those, 182 were classified as being definite cases, and 21 were probable cases, yielding a PPV of 90.6% (95% confidence interval [CI]: 86.0-94.1). The PPV decreased from 95.7% in patients aged 15-39 years to 87.5% in patients aged 80 years and over but was uniformly high regardless of study period, hospital or department type, or cause of empyema. CONCLUSION Our finding of a high overall PPV indicated good agreement between ICD-10 codes for pleural empyema and medical records. Registry-based discharge codes may be a suitable source of data on pleural empyema for epidemiological research.