Colorectal Cancer Screening (PDQ®): Screening - Health Professional Information [NCI] - Evidence of Benefit
Table 3. Randomized Controlled Screening Trials: Fecal Occult Blood Testing
|Site||Population Size||Positivity Rate (%)||% Cancers Localizeda||Testing Interval||Relative Mortality Reduction|
|a % Localized = T1-3 N0 M0.|
|United Kingdom||150,000||Unrehydrated: 2.1%||52||44||Biennial||15%|
Newer FOBTs: Nonrandomized Controlled Trial Evidence
The immunochemical FOBT (iFOBT) was developed to detect intact human hemoglobin. The advantage of iFOBT over gFOBT is that it does not detect hemoglobin from nonhuman dietary sources. It also does not detect partly digested human hemoglobin that comes from the upper respiratory or GI tract. Preliminary studies of several commercially developed iFOBT tests define their sensitivity and specificity compared with concurrently performed colonoscopy. These studies also examine these outcomes for different cut points, and the benefit of multiple versus single stool samples. Generally, iFOBT testing is more sensitive for cancers than for benign neoplasias. As expected, higher cut points decrease sensitivity and increase specificity.
In one study, 2,188 patients scheduled for colonoscopy because of an elevated risk due to personal or family history of colorectal neoplasm, positive gFOBT result, change in bowel habits, anemia, abdominal pain with weight loss, or anal symptoms were invited to participate in a comparative assessment of iFOBT against colonoscopy findings. After exclusions for health and cognitive reasons, 1,859 patients were offered iFOBT, 1,116 patients adhered to the protocol, and 1,000 patients completed the procedure. Sensitivity and specificity were calculated at various cut-points. At a cut-point of 100 ng/mL, sensitivity and specificity were, respectively, 88.2% and 89.7% for cancer and 61.5% and 91.4% for any clinically significant neoplasia (cancer and advanced polyps). At 150 ng/mL the respective sensitivities and specificities were 82.4% and 91.9% for cancer and 53.8% and 95% for any clinically significant neoplasia. Calculations were based on the most severe pathologic finding from colonoscopy and the highest fecal-hemoglobin concentration measured by iFOBT applied to three stool samples collected prior to the colonoscopy. Stool samples were collected by patients following iFOBT kit instructions and analyzed by the OC-MICRO analyzer (from the Eiken Chemical Company in Tokyo, Japan).