Double FIT-positive test flags higher likelihood of colorectal cancer

Patients who test positive on two faecal immunochemical tests (FITs) are several times as likely as those with only a single FIT-positive test to have colorectal cancer (CRC) or premalignant polyps, as shown in a local study.

“Singapore has adopted two-sample FIT in its national CRC screening program, as this has been shown to increase sensitivity by potentially detecting neoplasms that may have been missed in one-sample FIT,” according to a team of researchers from the National University of Singapore. [https://www.healthhub.sg/programmes/61/Screen_for_Life; Can J Gastroenterol Hepatol 2016;2016:5914048]

In a cohort of 1,345 single and 327 double FIT-positive individuals (median age overall 66 years) referred to a hospital for follow-up consultation and diagnostic colonoscopy, the incidence density of CRC was significantly higher among the latter at 13.10 per 100,000 person-months as opposed to 1.15 per 100,000 person-months among the former. [PLoS One 2021;16:e0250460]

The resulting incidence rate ratio for CRC was 11.40 (95 percent confidence interval [CI], 4.34–35.09).

Premalignant polyps, the most common colonoscopic finding, were likewise detected with greater frequency in the double than the single FIT-positive group (103 out of 173 vs 279 out of 671). This indicated that a double FIT-positive test had a higher positive predictive value (59.5 percent vs 41.6 percent; p<0.01).

In light of the findings, the researchers stressed that colonoscopy be expedited for individuals with double FIT-positive results to ensure prompt detection of CRC and premalignant polyps. This should help prevent bombardment of healthcare systems with limited facilities for colonoscopy by prioritizing which patients should more urgently undergo the procedure, especially if uptake for CRC screening with FIT increases.

“At the national level, countries that are still advocating CRC screening using only one-sample FIT should reconsider their approach. Double FIT-positive is likely to have increased specificity, resulting in fewer false positive findings during follow-up,” the researchers pointed out. [Gut 2013;62:727; Can J Gastroenterol Hepatol 2016;2016:5914048]

“Although compliance rates of individuals performing two-sample FIT over two separate days are likely to be slightly lower than one-sample FIT, this can be managed through public education and targeted interventions,” they said. “Countries concerned about costs to the health system should consider performing a cost-effectiveness analysis, which will likely favour a two-sample FIT program.” [Gut 2013;62:727]

More importantly, the low colonoscopy compliance rate observed in the current study and the literature—about 50 percent—points to a need to reinforce the importance of prompt follow-up after a positive FIT result, the researchers noted. [J Public Health 2018;40:e46-e58]

“Using simple arithmetic, another 33 CRC cases could have been diagnosed and managed promptly from our cohort should there have been perfect compliance. Prior literature has suggested a combination of patient and provider factors influencing follow-up compliance,” they said. [J Public Health 2018;40:e46-e58]

Developing tailored, cost-effective interventions aimed at improving compliance to follow-up colonoscopy should address the target population-specific barriers and facilitators, according to the researchers. “This can be achieved through a process evaluation to pinpoint specific interventions from referral at the national screening level, to the arrival at the clinic for the medical consultation, and [then at] the colonoscopic evaluation.”

The study was limited by its relatively small cohort derived from a single tertiary hospital, which could be attributed to the limited number of incident cases that in turn resulted in comparatively imprecise CIs.