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Fecal Occult Blood Testing

Which Test?

Occult Gastrointestinal (GI) Bleeding: Definition

Slide 2

October 2011

Let’s start with some basic concepts. By definition, occult GI bleeding is hidden or unseen. It may be surprising…but we all lose blood through our GI tract daily, as is shown in this plot of the distribution of fecal blood levels quantified by HemoQuant on specimens from 1000 consecutive asymptomatic Mayo Clinic patients. As you can see, occult bleeding is not present or absent….but rather occurs along a continuum from normal physiologic bleeding to abnormal bleeding. This “physiologic” blood loss averages less than 2mL/day. Levels above a 2mL/day threshold occur in 5% and are considered abnormal. If blood loss chronically exceeds 5mL/day, iron deficiency ensues. So, at what level does bleeding become visible or overt?

Occult Gastrointestinal (GI) Bleeding: Definition


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