Home stool test will detect most colorectal cancers

Fecal immunochemical tests (FITs) have high accuracy, high specificity and moderately high sensitivity and can detect about 4 out of 5 colorectal cancers, according to an evidence review.

Researchers reviewed 19 published studies of 8 different brands of FITs to determine their diagnostic accuracy for colorectal cancer and to identify factors affecting their performance characteristics. (Two brands have been discontinued and are no longer produced in the United States.)

Results appeared in the Feb. 4 Annals of Internal Medicine.

The overall accuracy of FIT was 95% (95% CI, 93% to 97%). Among the pooled results, on average, the FITs were sensitive (0.79; 95% CI, 0.69 to 0.86) to colorectal cancers with only one round of testing. The tests were also highly specific (0.94; 95% CI, 0.92 to 0.95). The positive likelihood ratio was 13.10 (95% CI, 10.49 to 16.35), and the negative likelihood ratio was 0.23 (95% CI, 0.15 to 0.33). (A positive likelihood ratio greater than 5 and a negative likelihood ratio less than 0.2 provide strong diagnostic evidence to rule in or rule out diagnoses.)

No brand performed markedly better than another, although the confidence intervals were fairly wide for sensitivity. The authors cautioned that only 2 brands had several studies that could be pooled in a subgroup analyses and that there was only 1 study comparing brands head-to-head. While most of the FITs required collection of only 1 stool sample, brands that required 2 or 3 stool samples were no more accurate than those requiring only 1 sample.

The authors noted that FIT type could be customized to different-sized care settings without significant variability in accuracy, allowing health systems wishing to optimize use to balance tradeoffs between increasing sensitivity by lowering the cutoff threshold for a positive test and the resulting increase in the number of positive test results.

A FIT cutoff value less than 20 µg/g had the best combination of sensitivity (89%) and specificity (91%) for colorectal cancer and the lowest negative likelihood ratio (0.16) compared with the subgroups with cutoff values of 20 to 50 µg/g and greater than 50 µg/g. However, studies using a 1-sample FIT with cutoff values less than 20 µg/g had positivity rates that were generally greater than those for 1-sample FITs at cutoff values of 20 to 50 µg/g.

“Considering the lack of colonoscopy resources across the world, identifying an optimal cutoff value for defining a positive result deserves considerable attention because this number can influence both the number of cancer cases detected as well as the number of colonoscopies needed in a [colorectal cancer] screening program,” the authors wrote.