research approaches. additionally, clinical studies look at a variety of additional factors. gastrointestinal blood loss in healthy people about 0.5 to 1.5 ml of blood escapes blood vessels into the stool each day. significant amounts of blood can be lost without producing visible blood in the stool, estimated as 200 ml in the stomach, 100 ml in the duodenum, and lesser amounts in the lower intestine. tests for occult blood identify lesser blood loss. clinical sensitivity and specificity fecal immunochemical testing (fit) can identify as little as 0.3 ml of daily blood in the stool; yet this test threshold doesn't cause undue false positives from normal upper intestinal blood leakage because it does not detect occult blood from the stomach and upper small intestine. thus, the fit test is much more specific for bleeding from the colon or lower gastrointestinal tract than alternatives. the detection rate of the test decreases if the time from sample collection to laboratory processing is delayed; processing the sample in under five days from collection is recommended. it does not appear to be affected by aspirin, anticoagulants, or nonsteroidal anti-inflammatory drugs. stool guaiac test for fecal occult blood (gfobt) sensitivity varies depending on the site of bleeding. moderately sensitive gfobt can pick up a daily blood loss of about 10 ml (about two teaspoonfuls), and higher sensitivity gfobt can pick up lesser amounts, requires at least 2 ml to become positive. the sensitivity of a single-stool guaiac test to pick up bleeding has been quoted at 10 to 30%, but if a standard three tests are done as recommended the sensitivity rises to 92%. reduced patient compliance with the collection of three samples hampers the usefulness of this test. further discussion of sensitivity and specificity issues that relate particularly to the guaiac method is found in the stool guaiac test article. fecal porphyrin quantification by hemoquant can yield a false positive result due to exogenous blood and various porphyrins. hemoquant is the most sensitive test for upper gastrointestinal bleeding and therefore may be most appropriate fecal occult blood test to use in the evaluation of iron deficiency. it is advisable to stop ingesting red meat and aspirin for three days prior to specimen collection. false positives can occur with myoglobin, catalase, or protohemes and in certain types of porphyria. fecal dna tests as of 2008 had not been studied enough to support widespread use. regulation safety regulations from us accreditor the joint commission may have unintentionally decreased digital rectal examination and fobt in hospital settings such as emergency departments.