931 Attendance and Diagnostic Yield of One Versus Two-Sample Fecal Immunochemical Test (FIT) Screening; a Comparative Population-Based Colorectal Cancer Trial

Abstract

Background Fecal Immunochemical Tests (FITs) are widely used for Colorectal Cancer (CRC) screening. Some sampling schemes use one-day FIT testing, whereas others use twoday FIT testing. Data on sensitivity and specificity of two-day FIT testing are lacking. This study aims to compare the difference in sensitivity and specificity of three different strategies of two-day FIT sampling, at different cut-off values. Methods In three hospitals in the Amsterdam area, all subjects ≥18 years who were referred for elective colonoscopy were asked to perform a FIT (OC sensor®) on two consecutive days. Colonoscopy and histology were considered as gold standard. Two-day FIT sampling was defined positive in three different ways: 1) when at least one of two FITs was above the cut-off value (FIT+), 2) when both FITs were above the cut-off value(FIT++), and 3) when the geometric mean of two FITs was above the cut-off value (FITmean). Test performance of all three strategies was evaluated at cut-off values of 50, 75 and 100ng/ml. Results In 1105 subjects with complete colonoscopy, 140 (9,4%) AN were found (34 CRCs and 106 advanced adenomas). Of the CRC cases, 70% were Dukes stage A or B (stage unknown in 2). Positivity rates for FIT+ ranged from 16-23%, for FIT++ from 10-13% and for FITmean from 13-17% (see table). At any cut-off level, FIT++ resulted in the lowest and FIT+ in the highest sensitivity. FIT++ showed a higher specificity than both other strategies (see table). Conclusions The most sensitive strategy in two-day FIT sampling is defining the test positive when at least one of both FITs passes the cut off (FIT+), whereas the highest specificity is obtained when both FITs need to be positive for calling the tests positive (FIT++). At all cut-off values, FITmean offers substantially better specificity than FIT+, while sensitivity is substantially higher than FIT++. Sensitivity and specificity of three methods to use two-day FIT sampling for the detection of advanced neoplasia