Validity and completeness of colorectal cancer diagnoses in a primary care database in the United Kingdom

PURPOSE: To validate the recorded diagnoses of colorectal cancer (CRC) and identify false negatives in The Health Improvement Network (THIN) primary care database. METHODS: We conducted a validation study of incident CRC cases in THIN among patients aged 40–89 years from 2000–2011. CRC Read code entries (N = 3805) were verified by manual review of patients' electronic medical records (EMRs) including free‐text comments. Incident CRC cases in THIN ascertained following manual review were validated against two data sources deemed gold standards: (i) questionnaires sent to primary care practitioners (PCPs; for a random sample of 100 potential CRC cases), and (ii) Hospital Episode Statistics (HES) among linked practices. False negatives in THIN were identified by searching for International Classification of Diseases‐10 codes related to CRC in HES. RESULTS: Of 3805 CRC cases identified in THIN via Read codes, 3033 patients (80.0%) were considered definite cases after manual review of EMRs. The positive predictive value (PPV) of CRC Read codes was 86.0% after removing patients identified from THIN via a Read code for ‘fast track referral for suspected CRC’. The response rate from PCPs was 87.0% (n = 87), and the PPV of CRC in THIN was 100% based on PCP questionnaires. Using HES, the PPV for CRC in THIN was 97.9% (556/568), and false negative rate was 6.1% (36/592). CONCLUSIONS: CRC diagnostic Read codes in THIN have a high PPV, which is increased further following manual review of free‐text comments. The false negative rate of CRC diagnoses in THIN is low. © 2015 The Authors. Pharmacoepidemiology and Drug Safety published by John Wiley & Sons Ltd.