What is the sensitivity and specificity of guaiac testing for fecal blood?
The sensitivity of guaiac testing depends on the specific brand used. Several guaiac reagents are marketed. The most sensitive brand is the Hemoccult II-SENSA test.
The sensitivity also depends on the lesion to be detected. It is not a good test for detecting colonic adenomas because adenomas infrequently bleed.
It is moderately (up to 80%) sensitive at detecting colon cancer when performed on 3 consecutive days to account for intermittent bleeding from colon cancer.
The specificity of guaiac testing is only approximately 20% to 30% for detecting significant colonic lesions.
The yield of colonoscopy performed for a guaiac-positive test is colon cancer in 3% to 4% of patients and colonic adenomas in 15% to 20% of patients (or higher in older adult patients).