Immunochemical fecal occult blood testing is equally sensitive for proximal and distal advanced neoplasia

Fecal immunochemical testing (FIT) is increasingly used for colorectal cancer (CRC) screening. We aimed to estimate its diagnostic accuracy in invitational population screening measured against colonoscopy.

Participants (50-75 years) in an invitational primary colonoscopy screening program were asked to complete one sample FIT before colonoscopy. We estimated FIT sensitivity, specificity, and predictive values in detecting CRC and advanced neoplasia (carcinomas and advanced adenomas) for cutoff levels of 50 (FIT50), 75 (FIT75), and 100 (FIT100) ng hemoglobin (Hb)/ml, corresponding with, respectively, 10, 15 and 20 μg Hb/g feces.

A total of 1,256 participants underwent a FIT and screening colonoscopy. Advanced neoplasia was detected by colonoscopy in 119 (9%), 8 (0.6%) of them had CRC. At FIT50, 121 (10%) had a positive test result; 45 (37%) had advanced neoplasia and 7 (6%) had CRC. A total of 74 of 1,135 FIT50 negatives (7%) had advanced neoplasia including 1 (0.1%) CRC. FIT50 had a sensitivity of 38% (95% confidence interval (CI): 29-47) for advanced neoplasia and 88% (95% CI: 37-99) for CRC at a specificity of 93% (95% CI: 92-95) and 91% (95% CI: 89-92), respectively. The positive and negative predictive values for FIT50 were 6% (95% CI: 3-12) and almost 100% (95% CI: 99-100) for CRC, and 37% (95% CI: 29-46) and 93% (95% CI: 92-95) for advanced neoplasia. The sensitivity and specificity of FIT75 for advanced neoplasia were 33% (95% CI: 25-42) and 96% (95% CI: 94-97). At FIT100, 71 screenees (6%) had a positive test result. The sensitivity and specificity of FIT100 were for advanced neoplasia 31% (95% CI: 23-40) and 97% (95% CI: 96-98), and for CRC 75% (95% CI: 36-96) and 95% (95% CI: 93-96). The area under curve for detecting advanced neoplasia was 0.70 (95% CI: 0.64-0.76). FIT had a similar sensitivity for proximal and distal advanced neoplasia at cutoffs of 50 (38% vs. 37%; P=0.99), 75 (33% vs. 31%; P=0.85) and 100 (33% vs. 29%; P=0.68) ng Hb/ml.

Nine out of ten screening participants with CRC and four out of ten with advanced neoplasia will be detected using one single FIT at low cutoff. Sensitivity in detecting proximal and distal advanced neoplasia is comparable.