[Diagnostic performance of quantitative fecal immunochemical test in detection of advanced colorectal neoplasia]

Objective: To evaluate the diagnostic performance of quantitative fecal immunochemical testing (FIT) and to provide reference for designing effective colorectal cancer (CRC) screening strategy in China. Methods: Based on an ongoing randomized controlled trial comparing the colorectal cancer screening strategies, this current study involved 3 407 participants aged 50-74 years who had undergone colonoscopies. All the feces samples were collected from the participants prior to receiving the colonoscopy. Fecal hemoglobin (Hb) was tested by FIT following a standardized operation process. Diagnosis-related indicators of FIT were calculated using the colonoscopy results as the gold standard. Results: Among the 3 407 participants, the mean age (SD) as 60.5 (6.3) years and 1 753 (51.5%) were males. The participants involved 28 (0.8%) CRCs, 255 (7.5%) advanced adenomas, 677 (19.9%) nonadvanced adenomas, and 2 447 (71.8%) benign or negative findings. With an overall positivity rate of 2.8% (96/3 407) at the recommended cutoff value of 20 μg Hb/g, the sensitivities of FIT for both CRC and advanced adenoma were 57.1% (95%CI: 37.2%-75.5%) and 11.0% (95%CI: 7.4%-15.5%), respectively, with the corresponding specificity as 98.4% (95%CI: 97.8%-98.8%). At a decreased cut-off value of 5 μg Hb/g, the sensitivities for detecting CRC and advanced adenoma increased to 64.3% (95%CI: 44.1%-81.4%) and 16.5% (95%CI: 12.1%-21.6%), respectively, but the specificity reduced to 95.2% (95%CI: 94.4%-95.9%). The areas under the ROC curve for CRC and advanced adenoma were 0.908 (95%CI: 0.842-0.973) and 0.657 (95%CI: 0.621-0.692), respectively. Of the diagnostic performance, there were no significant differences noticed by different sex and age groups. Conclusions: In our study, the quantitative FIT showed modest sensitivity in detecting CRC but limited sensitivity in detecting advanced adenoma. In population-based CRC screening programs, the quantitative FIT had the advantage of adjusting the positive threshold based on the targeted detection rate and available resource load of colonoscopy.