Accuracy of Fecal Immunochemical Tests for Diagnosis of Colorectal Cancer

For evaluation of patients with new-onset lower gastrointestinal symptoms, fecal immunochemical tests (FIT) are the preferred choice in primary healthcare, according to study results published in the journal Gut.

In a systematic review of the Medline and EMBASE databases from May 2018 to November 2020, 22 studies including 69,536 participants met the criteria for this review and meta-analysis. These studies included adult patients undergoing consultation for abdominal symptoms in a primary care setting. Reported data was used to assess the diagnostic performance parameters of FIT for colorectal cancers.

Among these studies, the prevalence of colorectal cancer ranged from 0.3% to 6.2%. In terms of accuracy of FIT based on positivity thresholds to detect colorectal cancer, the limit of detection value depended on the brand of FIT used. Overall pooled sensitivity and specificity for studies using the limit of detection as a threshold were 93.4% (95% CI, 88.0%-96.4%) and 76.9% (95% CI, 67.7%-84.0%), respectively.

For studies with a threshold of ≥10 µg Hb/g feces, the sensitivity for colorectal cancer was 87.2% (95% CI, 81.0%-91.6%) and decreased to 84.1% (95% CI, 78.6%-88.4%) for studies with a threshold ≥20 μg Hb/g feces. The specificity increased from 84.4% (95% CI, 79.4%-88.3%) to 86.6% (95% CI, 75.6%-93.1%).

Six studies evaluating the accuracy of FIT with a threshold of ≥150 μg Hb/g feces in 34,691 patients reported a sensitivity and specificity of 64.1% (95% CI, 57.8%-69.9%) and 95.0% (95% CI, 91.2%-97.2%), respectively.

According to researchers, the minor differences observed between thresholds of 10 µg Hb/g feces and 20 μg Hb/g feces indicate that <1 additional case of colorectal cancer would be missed per 1000 patients investigated when choosing the higher threshold.

Limitations included the potential for clinical spectrum bias in studies that recruited patients in colonoscopy units. Additionally, there was a risk of poor representativeness due to the low ratio between eligible patients and those included in the final analysis of some studies.

According to researchers, this study, “confirmed that implementation of FIT as a triage test in primary care may improve the efficiency of referrals.” They added, “Use of this test as ‘rule in’ at a cut-off value of 150 μg Hb/g feces identifies more than half of [colorectal cancers] using few resources while [a fecal hemoglobin] concentration below 20 μg Hb/g feces rules out more than 85% of [colorectal cancers] at the expected prevalence in this setting (1%–3%).”

Reference

Pin-Vieito N, Tejido-Sandoval C, de Vicente-Bielza N, Sánchez-Gómez C, Cubiella J. Faecal immunochemical tests safely enhance rational use of resources during the assessment of suspected symptomatic colorectal cancer in primary care: systematic review and meta-analysis. Gut. Published online June 9, 2021. doi:10.1136/gutjnl-2021-324856