Accuracy of pneumonia hospital admissions in a primary care electronic medical record database

PURPOSE: When using electronic medical record data to study drug use, hospitalizations are markers of severe outcomes. To identify events within a specified time window, it is important to validate hospitalization diagnoses and dates. Our objective was to validate pneumonia hospitalizations and their dates identified using hospitalization codes in The Health Improvement Network (THIN), a UK primary care electronic medical record. METHODS: This cross-sectional study used a cohort of THIN adult visits for acute nonspecific respiratory infections from June 1985 to August 2006. Pneumonia hospitalizations within 30 days after the visit were identified using THIN diagnosis and hospitalization codes; 60 participants were randomly selected for validation. Patients' general practitioners (GPs) returned de-identified hospital summaries and consultants' letters regarding overnight hospitalizations within a 180-day window around the THIN hospitalization. Positive predictive value (PPV) was the number of GP-validated hospitalizations divided by THIN documented hospitalizations. RESULTS: GPs returned 59 of 60 patient records; 52 had confirmed hospitalizations. PPV of THIN hospitalization documentation was 88% (95%CI = 77-95). One admission was not for pneumonia; PPV of THIN-documented pneumonia admission was 86% (95%CI = 75-94). Of 52 valid THIN hospitalizations, 50 were actually admitted within 14 days of the documented THIN date (range = -2 to +18). The absolute median difference between THIN and validated admission dates was +0.5 days, and the absolute mean difference was +3.1 days. In 16 of 52 admitted patients, the THIN admission date was the actual discharge date. CONCLUSIONS: THIN hospitalization codes performed well in identifying acute pneumonia hospitalizations and their timing. Admission date validity might be better for conditions associated with shorter versus longer hospitalizations.