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

Abstract

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 40-89years 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.