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Quantitative Fecal Occult Blood Testing Promising

A noninvasive screening test for colorectal cancer would be useful.

Guaiac-based fecal occult blood tests (FOBTs) are nonspecific and insensitive. Researchers with support from the maker of a quantitative immunochemical FOBT specific for human hemoglobin tested its performance in 1000 ambulatory adults undergoing elective colonoscopy. Some patients were asymptomatic, some were at high risk for cancer, and some were symptomatic.

At colonoscopy, cancer was detected in 17 patients, and advanced polyps in 74. Fecal hemoglobin concentrations were significantly higher in these patients than in others. A fecal hemoglobin threshold of 75 ng/dL (as measured in 3 samples) was used to define an abnormal result; at this level, the immunochemical FOBT had a sensitivity of 67% and specificity of 91% for advanced neoplasia. For cancer, sensitivity and specificity were 94% and 88%.

Comment: Because the quantitative immunochemical FOBT appears to have reasonable sensitivity and specificity for a screening test, some people might use it to select patients for colonoscopy. But people who desire greater certainty will likely forgo this test, as they forgo the guaiac-based tests. An editorialist recommends that quantitative FOBTs be preferred to guaiac-based tests whenever an FOBT is a component of a screening strategy. In the U.S., some currently available immunochemical FOBTs can be reported quantitatively, but they are not generally used that way yet.

— Richard Saitz, MD, MPH, FACP, FASAM

Published in Journal Watch General Medicine March 22, 2007

Citation(s):

Levi Z et al. A quantitative immunochemical fecal occult blood test for colorectal neoplasia. Ann Intern Med 2007 Feb 20; 146:244-55.

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Imperiale TF. Quantitative immunochemical fecal occult blood tests: Is it time to go back to the future? Ann Intern Med 2007 Feb 20; 146:309-11.

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• Medline abstract (Free)