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Positive fecal occult blood test (FOBT), fecal immunochemical test (FIT), or iron deficiency anemia in an adult with no visible fecal blood loss
2–6% of patients in screening programs have a positive FOBT or FIT
2% of men and 5% of women have iron deficiency anemia
Origin of occult bleeding is unexplained in 30–50% of patients
In premenopausal women
In men and postmenopausal women
Colonic blood loss in 15–30%
Upper GI blood loss in 35–55%
Malignancy in the lower gastrointestinal tract in 8.9% and upper tract in 2.0%
Most common causes of occult blood loss
Neoplasms
Vascular abnormalities (angioectasias)
Acid-peptic lesions
Infections (nematodes [especially hookworm], tuberculosis)
Medications (especially NSAIDs or aspirin)
Inflammatory bowel disorder or malabsorption (celiac disease)
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Colonoscopy with or without upper endoscopy is indicated
For all adults with positive FOBT or FIT test or iron deficiency anemia
For premenopausal women and younger men with GI symptoms
For those with family history of GI cancer
For women with anemia disproportionate to the estimated menstrual blood loss
Colonoscopy should be done first unless upper GI tract symptoms are present
Further investigation of the small intestine is recommended in patients who have
Anemia that responds poorly to empiric iron supplementation
Signs of ongoing bleeding (fecal occult blood)
Worrisome symptoms (abdominal pain, weight loss)
Capsule endoscopy is recommended as the initial study in most patients to look for vascular ectasias and to exclude a small intestinal neoplasia or inflammatory bowel disease
If a small intestine source is identified, push enteroscopy, balloon-assisted enteroscopy, abdominal CT, angiography, or laparotomy are pursued, as indicated
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Colonoscopy, upper endoscopy, and small bowel enteroscopy allow
Biopsy specimens to be obtained
Benign and malignant neoplasms to be excluded
Vascular ectasias to be cauterized endoscopically
For patients with iron deficiency anemia who have no significant findings on upper endoscopy or colonoscopy and who are without symptoms of small intestinal disease,
An initial trial of empiric iron therapy is recommended by the 2020 American Gastroenterological Association guidelines
Once daily administration of oral formulations containing 150 mg of elemental iron commonly recommended
However, lower daily doses (60–100 mg) or alternate day dosing may be better tolerated and are equally efficacious
A sustained rise in ferritin and hemoglobin with 1–2 months of iron therapy may obviate the need for further studies