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Fecal Occult Blood Testing

Which Test?

Quantity of GI Bleeding Required to "See" Blood in Stool

Slide 3

October 2011

The answer is that it depends. It depends on both the anatomic source and rate of bleeding. Large amounts of blood can be lost from upper GI sites and remain occult. Based on a number of observational studies with quantitative fecal blood tests, it takes more than 200mL/day for gastric bleeding to be uniformly overt, 150 mL/day from the cecum, 5-30 from the rectosigmoid, and just trace amounts from the anal canal (such as can commonly occur with hemorrhoids). So, bleeding rates can far exceed that required to produce iron deficiency and yet remain occult.

Quantity of GI Bleeding Required to "See" Blood


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