False-positive results from colorectal cancer screening in Catalonia (Spain), 2000-2010

Objective To identify factors associated with a false-positive result in a population-based colorectal cancer (CRC) screening programme with the faecal occult blood test (FOBT) in Catalonia between 2000 and 2010. Methods The study population consisted of participants of the Catalan CRC screening programme with a positive FOBT who underwent a colonoscopy for diagnostic confirmation from 2000 to 2010. A false-positive result was defined as having a positive test but detecting no high-risk adenoma or cancer in the follow-up colonoscopy. Multivariate logistic regression models were performed to identify sociodemographic and screening variables related to false-positive results. Adjusted odds ratios (OR) and their 95% confidence intervals (CI) were estimated. Results Over the screening period, 1074 (1.7%) of the 63,332 screening tests had a positive result in the Catalan CRC screening programme. The false-positive proportion was 55.2% (n = 546). Women were more likely to have a positive FOBT in the absence of CRC neoplasia than men (adjusted OR = 2.91; 95% CI: 2.22–3.28). During the first prevalence round, the proportion of false-positive results was higher than in subsequent rounds (69.5% vs. 48.9%; P < 0.05). Re-screening and having a bleeding pathology such as haemorrhoids or anal fissures were also associated with a false-positive result. Conclusion The proportion of false-positive results and the associated risks should be estimated to provide an eligible population with more reliable information on the adverse effects of screening.