930 Comparing Three Different Strategies of Double Sampling by Fecal Immunochemical Tests for Detection of Advanced Colorectal Neoplasm's

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