Fecal Immunochemical Test Positivity Thresholds: An International Survey of Population-Based Screening Programs

The fecal immunochemical test for hemoglobin (FIT) is now a widely used non-invasive test in population-based organized screening programs for colorectal neoplasia. The positivity thresholds of tests currently in use are based on the fecal hemoglobin concentration (f-Hb), but the rationale for the adopted thresholds are not well documented. To understand current global usage of FIT in screening programs we conducted an international survey of the brands of FIT used, the f-Hb positivity threshold applied and the rationale for the choice.

All members of the World Endoscopy Organization CRC Screening Committee were invited to complete an eight-element initial electronic survey exploring the key aims. Responses were obtained from 63 individuals, representing 38 specific locations in 28 countries. A follow-up survey on technical issues was offered to the 38 locations, with replies from 17 sites in 13 countries.

In-use quantitative FIT were provided by four main manufacturers; Minaris Medical (2 countries), Eiken Chemical Company/Polymedco (21), Alfresa Pharma (2) and Sentinel Diagnostics (4). Of the 38 screening sites, 15 used the threshold of 20 µg hemoglobin/g feces, while thresholds ranged between 8.5 and 120 ug/g in the remainder. Seven explanations were given for adopted FIT thresholds; maximizing the sensitivity for colorectal neoplasia (n = 23) was the most common followed by the availability of colonoscopy resources (n = 18). Predictive value, specificity, and cost effectiveness were less frequently reported as the rationale. Nine sites found it necessary to change the threshold that they had initially selected.

This international survey has documented the wide range of FIT positivity thresholds that are in current use. Quantitative FITs enable programs to achieve the desired program outcomes within available resource constraints by adjusting the positivity threshold. This supports the need for enabling positivity threshold adjustment of emerging new screening tests based on novel predictive biomarkers, rather than providing inflexible test endpoints.