Differential Diagnosis of Occult Gastrointestinal Bleeding
Mass lesions
- carcinoma of any site
- large (more than 1.5 cm) adenomatous polyp
Inflammation
- erosive esophagitis
- ulcer of any site
- linear cuts in a hiatus hernia
- erosive gastritis
- celiac disease
- ulcerative colitis
- Crohn's disease (regional enteritis)
- nonspecific colitis
- unexplained cecal ulcer
Vascular disorders
- vascular ectasia (blood vessel inflammation)
- liver vein hypertension
- gastrointestinal varicose veins (varices)
- other blood vessel abnormalities
Infectious diseases
- hookworm
- whipworm
- strongyloidiasis
- ascariasis
- tuberculous enterocolitis
- amebiasis
Other causes
- coughing blood from lungs and swallowing it
- nosebleeds and mouth cavity bleeding
- pancreatitis
- long distance running
- falsified causes
I have heard iron supplementation and sometimes aspirin can cause a false positive test. Is that true?
Many people believe that oral iron medications cause a false positive fecal blood test. They really do not. The only problem is that it may confuse someone in reading the test because the dark green or black appearance of iron in the stool may may be mistaken for the blue color typical of a positive guiac test.
Another misconception is that aspirin or anticoagulants often cause GI tract bleeding. While it is possible that this happens on some occasions, it is actually infrequent, i.e., most patients on anticoagulants or aspirin do not have guiac detectable fecal blood levels.
Some studies of patients on anticoagulants who had positive fecal occult blood tests show over 90% causes from major gastrointestinal conditions rather than just due to the anticoagulants.
There are occasionally other causes of false positive fecal occult blood tests that are from ingested substances. Any hemoglobin/blood in red meat can affect the test as well as some vegetable enzymes on occasion
Is there a relationship between iron deficiency anemia and gastrointestinal bleeding?
Iron deficiency anemia is usually diagnosed by a hemoglobin value of less than 12 g/dl and a serum ferritin level of less than 45 ug/l. In the U.S., 5-11% of women have iron deficiency anemia, often on a basis of menstrual bleeding problems. However, chronic occult gastrointestinal bleeding is also a frequent cause of iron deficiency.
Anytime a woman is diagnosed with anemia and it turns out to be of the iron deficient form, an investigation should be made to make sure the blood loss is not from somewhere other than menses.
At a minimum, a test for fecal occult blood should be performed. As much as 12% of iron deficiency anemia in premenopausal women may be due to serious gastrointestinal anomalies.
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