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Fecal Occult Blood Tests for Colorectal Cancer
- D. James B. St. John, MD; and
- Graeme P. Young, MD
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IN RESPONSE:
Drs. Singh and Gallo raise several practical concerns about occult blood testing, including the need to restrict diet and medications, to train the staff properly, and to avoid testing after dental extraction, during menstruation, or when hemorrhoids are bleeding. Nonetheless, they are unduly critical of the tests. In most large screening programs, Hemoccult positivity has ranged from 1% to 2.5% [1-3]. The special problem with nonhydrated Hemoccult is not its specificity [3] but its rather low sensitivity for colorectal cancer [1, 2]. Also, the predictive value of a positive test for cancer may be only 10%, but another 15% to 30% of middle-aged screenees prove to have large adenomas.
Alternatives to Hemoccult tests include guaiac tests with a higher level of sensitivity for hemoglobin, the heme-porphyrin assay, and immunochemical tests specific for human hemoglobin. The latter especially merit careful evaluation because diet and medication need not be changed. In addition, they have a high sensitivity for hemoglobin and are able to differentiate between bleeding from the upper and lower gastrointestinal tracts [4].
Furthermore, flexible sigmoidoscopy is not as advantageous as Singh and Gallo suggest because of the anatomical distribution of cancers in the large bowel. The theoretical sensitivity of flexible sigmoidoscopy for colorectal cancer can be no greater than 55% to 65% and may well be less in practice. Flexible sigmoidoscopy and fecal occult blood testing probably have complementary roles in screening. Meanwhile, the search for better occult blood tests should continue.
The Editors welcome submissions for possible publication in the Letters section. Authors of letters should:
•Include no more than 300 words of text, three authors, and five references
•Type with double-spacing
•Send three copies of the letter, an authors' form signed by all authors, and a cover letter describing any conflicts of interest related to the contents of the letter.
Letters commenting on an Annals article will be considered if they are received within 6 weeks of the time the article was published. Only some of the letters received can be published. Published letters are edited and may be shortened; tables and figures are included only selectively. Authors will be notified that the letter has been received. If the letter is selected for publication, the author will be notified about 3 weeks before the publication date. Unpublished letters cannot be returned.
Annals welcomes electronically submitted letters.
- Copyright ©2004 by the American College of Physicians
