Accuracy of Screening Tests

Sensitivity of screening with fecal occult blood testing (FOBT) varies with the frequency of testing and the method used. Sensitivity and specificity have been estimated at 40% and 96% to 98%, respectively. Hydration of the specimen increases sensitivity (60%) but reduces specificity (90%), producing more false-positive results (Pignone et al., 2002b).

Sigmoidoscopy visualizes only the lower half of the colon but has been estimated to identify 80% of all patients with significant findings in the colon because abnormal findings on sigmoidoscopy trigger examination of the entire colon (Pignone et al., 2002b). A colonoscopy has a sensitivity of 90% for large polyps and 75% for small polyps. Specificity for endoscopic screening is difficult to determine because many patients have polyps removed that would never have developed cancer. Newer stool study modalities with limited data include fecal DNA and fecal immunochemical tests.

Other screening tests for colorectal cancer include double-contrast barium enema, which has not reached the level of sensitivity of other modern screening procedures, and computed tomography (CT) colonography (i.e., virtual colonoscopy), which may have similar sensitivity as direct colonoscopy in finding colorectal cancer and large adenomas. Digital rectal examination (DRE) is not a recommended screening method for colorectal cancer because less than 10% of lesions are within the reach of an examiner's finger.

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