FIT Could Accurately Rule Out CRC in Symptomatic Patients

Fecal immunochemical testing (FIT) could be used to rule out colorectal cancer (CRC) in patients with suspected symptoms and fast-track those needing urgent care, a British double-blind diagnostic accuracy study suggested.

In an analysis of almost 10,000 patients referred to a specialist for suspected CRC symptoms that met criteria for urgent care, FIT sensitivity was maximized to 97.0% at the lowest fecal hemoglobin concentration cutoff of 2 µg/g, reported Muti Abulafi, MBBCh, of Croydon University Hospital in Basingstoke, England, and colleagues.

“A negative FIT result at this cutoff can effectively rule out CRC and a positive FIT result is better than symptoms to select patients for urgent investigations,” the group wrote in Gut.

CRC and other serious bowel disease is more likely at higher fecal hemoglobin concentrations.

No significant variation in FIT’s ability to detect CRC by patient or tumor characteristics, including age, sex, ethnicity, income, or iron-deficiency anemia were found in the study.

The findings follow a recent modeling study from Abulafi and colleagues that concluded that FIT could prioritize symptomatic primary-care patients for colonoscopy and circumvent delays caused by the COVID-19 pandemic.

Yamini Natarajan, MD, of Michael E. DeBakey VA Medical Center and Baylor College of Medicine in Houston, told MedPage Today that the results suggest a role for FIT in patients with symptoms such as rectal bleeding and anemia that may prompt evaluation for cancer with colonoscopy.

“This study demonstrated that use of FIT may be sufficient to rule out colon cancer as part of a care pathway,” said Natarajan, who was not involved in the research.

But while the findings show promise, particularly in the era of COVID-19 when cancer screenings have often been deferred, Natarajan urged caution in the evaluation of FIT sensitivity and the local prevalence of CRC. “Further studies should be done in the United States,” she said.

In the U.K., the National Institute for Health and Care Excellence (NICE) recommends FIT to guide referral of patients with low-risk bowel symptoms, at a fecal hemoglobin concentration cutoff of 10 μg/g, but it has not recommended it for all symptomatic patients owing to concerns about the quality and power of previous studies.

Study Details

The study from Abulafi and colleagues was conducted at 50 National Health Service (NHS) hospitals across England from 2017 to 2019. Eligible patients were those referred to secondary care with symptoms of suspected CRC meeting NHS criteria for urgent 2-week wait referrals. Triaged to investigation with colonoscopy, they were invited to have a quantitative FIT.

Median age was 65 in the final cohort of 9,822 kit-returning patients, 54% of whom were women. Incidence of CRC at colonoscopy was 3.3%. At fecal hemoglobin concentration cutoffs of 2, 10, and 150 µg/g, FIT positivity decreased from 37.2% to 19.0% and 7.6%, respectively.

The positive predictive values of FIT for CRC was 8.7% (95% CI 7.8-9.7) at the 2 µg/g cutoff, 16.1% (95% CI 14.4-17.8) at the 10 µg/g cutoff, and 31.1% (95% CI 27.8-34.6) at the 150 µg/g cutoff. Respective negative predictive values were 99.8% (95% CI 99.7-99.9), 99.6% (95% CI 99.5-99.7), and 98.9% (95% CI 98.7-99.1).

In terms of sensitivity for CRC, this decreased from 97.0% (95% CI 94.5-98.5) at the 2 µg/g cutoff, to 90.9% (95% CI 87.2-93.8) at the 10 µg/g cutoff, and 70.8% (95% CI 65.6-75.7) at the 150 µg/g cutoff. Specificity increased from 64.9% (95% CI 63.9-65.8) to 83.5% (95% CI 82.8-84.3) and 94.6% (95% CI 94.1-95.0), respectively.

According to the investigators, a higher hemoglobin cutoff could be set to match capacity in resource-limited settings, which would “reduce the number of positive results, onwards referral for investigation and demand for colonoscopy but at the expense of detecting fewer cancers.”