There are several terms used when describing chronic gastrointestinal blood loss . Obscure bleeding is defined as bleeding from the gastrointestinal tract that persists or recurs without an obvious etiology after upper endoscopy, colonoscopy, and radiologic evaluation of the small bowel (such as by small bowel follow-through or enteroclysis, though in practice, patients are typically diagnosed with obscure bleeding based on upper endoscopy and colonoscopy results alone without undergoing radiologic procedures). Obscure bleeding may be either overt or occult.
●Occult bleeding refers to a positive fecal occult blood test result that may or may not be associated with iron-deficiency anemia when there is no evidence of visible blood loss to the patient or clinician.
●Overt bleeding refers to bleeding that is visible to the patient or clinician. Obscure-overt bleeding may manifest as melena or hematochezia.
The evaluation of patients with obscure-occult and obscure-overt bleeding will be reviewed here. The initial evaluation of patients with gastrointestinal bleeding is discussed separately. (See "Evaluation of occult gastrointestinal bleeding" and "Approach to acute upper gastrointestinal bleeding in adults" and "Approach to acute lower gastrointestinal bleeding in adults".)
Obscure gastrointestinal bleeding accounts for approximately 5 percent of patients with gastrointestinal bleeding . This number has not been re-evaluated in the capsule era. In approximately 75 percent of these patients, the source is in the small bowel [3-6]. The remainder of cases are due to missed lesions in either the upper or lower gastrointestinal tract.