Correlation of Fecal Immunochemical Testing Levels With Pathology Results in a National Colorectal Cancer Screening Program

INTRODUCTION: Fecal immunochemical testing (FIT) positivity is determined by a threshold decided by individual screening programs. Data are limited on correlation between FIT levels and pathology identified at colonoscopy. Our aim was to examine the correlation between FIT levels and pathology identified in a national colorectal cancer screening program. METHODS: FIT levels (n = 9,271) were analyzed and correlated with patient demographics and pathology identified, including adenomas, sessile serrated lesions, number/size of adenomas, and presence of dysplasia. Levels were divided into 2 categories: FIT levels were defined as “high” or “low” based on whether they were above or below the median (479 ngHb/mL). Multivariate analysis was performed. RESULTS: A total of 8,084 patients (87%) underwent colonoscopy. Those younger than 65 years (odds ratio [OR] 1.267, 95% confidence interval [CI] 1.107–1.45, P = 0.001), those with an adenoma >10 mm (OR 1.736, 95% CI 01.512–1.991, P < 0.001), and those with left-sided adenomas (OR 1.484, 95% CI 1.266–1.74, P < 0.001) had higher FIT levels. Cancers (OR 2.8, 95% CI 2.09–3.75, P < 0.001) and high-grade dysplasia (OR 1.356, 95% CI 1.08–1.7, P = 0.008) had higher FIT levels, but varied greatly. The number of adenomas was not significant. DISCUSSION: In this study, FIT levels were high for left-sided and large adenomas, suggesting that FIT has poor sensitivity for detection of diminutive and right-sided neoplasia. FIT levels had no association with gender and declined with age. Adenoma burden did not correlate with FIT levels; this is a novel finding. FIT levels vary greatly even in those with advanced neoplasia; therefore, FIT is unlikely to be useful as a risk stratification tool.