FIT Assay Shows Overall Diagnostic Accuracy for CRC

Researchers have concluded from an analysis of multiple studies that the fecal immunochemical test (FIT) has high overall diagnostic accuracy for screening asymptomatic patients at an increased risk for colorectal cancer (CRC) and moderate accuracy for diagnosing advanced neoplasia (AN). The findings are important because colonoscopy is currently the only recommended screening modality for patients at increased risk of CRC, such as those with a personal or family history of CRC.

The purpose of the study was to investigate the value of using FIT as an alternative to colonoscopy in high-risk patients, because colonoscopy is invasive and expensive, and has an established risk of complications, and for these reasons, adherence is poor.

The meta-analysis included 12 studies consisting of 6204 participants. Across the studies, the mean ages of participants ranged from 46 to 63.2 years; the percentages of males ranged from 30.2% to 50.6%.

In the main analysis, the sensitivity and specificity of FIT for diagnosis of CRC ranged from 0.25 to 1.00 (median, 0.81) and from 0.87 to 0.95 (median, 0.91), respectively. The sensitivity and specificity for diagnosing AN ranged from 0.29 to 0.83 (median, 0.5) and 0.85 to 0.98 (median, 0.92), respectively.

Pooled estimates of sensitivity and specificity for CRC were 93% (95% CI, 53%-99%) and 91% (95% CI, 89%-92%), yielding a positive likelihood ratio (LR+) of 10.30 (95% CI, 7.7-13.9) and a negative likelihood ratio (LR-) of 0.08 (95% CI, 0.01-0.75). Positive and negative predictive values were 7.7% and 99.9%, respectively.

The pooled sensitivity and specificity for diagnosing AN were 48% (95% CI, 39%-57%) and 93% (95% CI, 91%-94%), respectively, yielding an LR+ of 6.5 (95% CI, 5-8.5) and an LR- of 0.57 (95%CI, 0.48-0.67). Positive and negative predictive values were 43.8% and 94%, respectively.

The study’s results suggest that given FIT’s safety, simplicity, low cost, and low discomfort, the test could be an acceptable alternative for screening of individuals at increased risk for CRC.

Additional subgroup analyses for quantitative FIT and 1-sample FIT test methods showed adequate performance; however, investigators did not have sufficient data to draw conclusions about qualitative FIT or the use of multiple samples.

The researchers noted that the quality and quantity of evidence they weighed was not ideal. Most of the studies had small sample sizes or low prevalence of CRC or AN. Three studies were prone to differential verification bias because they invited participants with negative FIT results to undergo a delayed colonoscopy as the reference standard.

Investigators stressed the need for future studies that include larger and better-defined patient populations, the establishment of optimal thresholds, test cutoff values, and guidelines for the number and frequency of FIT samples.

Katsoula A, Paschos P, Haidich AB, Tsapas A, Giouleme O. Diagnostic accuracy of fecal immunochemocal test in patients at increased risk for colorectal cancer: a meta-analysis. JAMA Intern Med. 2017;177(8):1110- 118. doi: 10.1001/jamainternmed.2017.2309.