Fecal immunochemical tests vary widely in sensitivity, specificity

Five common fecal immunochemical tests (FITs) varied substantially in their performance, a study found.

To compare the performance characteristics of commonly used FITs, with colonoscopy as a reference standard, researchers conducted a cross-sectional study at three U.S. academic medical centers and affiliated endoscopy units among patients ages 50 to 85 years who were undergoing screening or surveillance colonoscopy. Participants completed five FITs before their colonoscopy, including four qualitative tests (Hemoccult ICT, Hemosure iFOB, OC-Light S FIT, QuickVue iFOB) and one quantitative test (OC-Auto FIT). The primary outcome was sensitivity and specificity of each test for advanced colorectal neoplasia, defined as advanced polyps or colorectal cancer. Positivity rates, positive and negative predictive values, and rates of unevaluable tests were compared. The study was published Sept. 3 by Annals of Internal Medicine.

Among 3,761 study participants, 320 participants had advanced neoplasia (8.5%), including nine with colorectal cancer (0.2%). The test positivity rate varied from 3.9% to 16.4% across FITs. Rates of unevaluable tests ranged from 0.2% to 2.5%. The sensitivity for advanced neoplasia varied from 10.1% to 36.7%, and specificity varied from 85.5% to 96.6%. Differences in sensitivity between FITs were all statistically significantly different except between Hemosure iFOB and QuickVue iFOB, and all specificity differences were statistically significant from one another.

The automated OC-Auto FIT (with a cutoff of >100 ng/mL) had both the highest positive predictive value (28.9% [95% CI, 22.9% to 35.5%]) and the highest positive likelihood ratio (4.4 [95% CI, 3.2 to 5.6]) and could be considered by health systems with the capacity for automated testing, the study authors said. They also highlighted the finding that Hemoccult ICT and QuickVue iFOB had the highest proportion of unevaluable tests (2.3% and 2.5%, respectively, compared to less than 0.5% with the other tests).

Although FITs are considered a single class, they have varying test performance for detecting neoplasia and should not be considered interchangeable, the authors concluded. “Our findings have practical importance for FIT-based screening programs, as these differences affect the need for repeated FIT, the yield of [advanced colorectal neoplasia] detection, and the number of diagnostic colonoscopies that would be required to follow up on abnormal findings,” they wrote. “There is no consensus on the correct ratio of false-positive to false-negative results on FIT, and the answer may differ depending on the context, colonoscopy capacity, and resources.”