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Fecal Occult Blood Tests for Colorectal Cancer
- Paramvir Singh, MD; and
- Steven H. Gallo, MD
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TO THE EDITOR:
St. John and colleagues [1] deserve congratulations for their extensive study on the comparison of specificity and sensitivity of fecal occult blood testing (FOBT) methods in screening for colorectal neoplasia. They did not, however, adequately address the importance of the timing of the collection or the experience of the person doing it. As little as 5 mL of blood in the upper gastrointestinal tract (secondary to dental extraction and so forth) may produce positive FOBT results, and an inexperienced processor can increase screening positivity fourfold [2].
Although widely used, Hemoccult II results may be affected by dietary peroxidase, fecal hydration, and some drugs. False-positive results are seen in 3% to 7.5% of patients, with and without rehydration [3]. The predictive value of a positive FOBT for colorectal cancer, although used as an indicator for proceeding with colorectal investigation, may be only 10%. Consequently, most FOBT-positive patients subjected to colorectal investigations do not have cancer [4]. Conversely, a negative FOBT should not deter a diagnostic evaluation, if colorectal cancer is strongly suspected.
Furthermore, although subclinical colorectal cancer may be detected at a relatively early stage, whether the test actually improves long-term survival remains to be proved [4]. Moreover, differentiating between the upper and lower gastrointestinal tracts on the basis of FOBT results is not possible. Because of the imprecision of FOBT, flexible fiberoptic sigmoidoscopy continues to play a significant role in the screening of colorectal cancer in the asymptomatic population at risk [5].
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
