What is the next step for a patient with anemia and a positive fecal occult blood test (FOBT)?

Management of Anemia with Positive Fecal Occult Blood Test

Initial Diagnostic Approach

For a patient with anemia and a positive fecal occult blood test, bidirectional endoscopy (colonoscopy and upper endoscopy) is strongly recommended as the next step in evaluation.

The presence of both anemia and a positive fecal occult blood test strongly suggests gastrointestinal blood loss that requires thorough investigation to identify the source of bleeding.

Rationale for Bidirectional Endoscopy:

• Colonoscopy is the preferred initial diagnostic procedure for positive FOBT as it allows direct visualization of the entire colon and removal of polyps 1
• Dual pathology (lesions in both the upper and lower GI tracts) occurs in approximately 10-15% of patients with iron deficiency anemia, necessitating evaluation of both upper and lower GI tracts 2
• The American Gastroenterological Association (AGA) strongly recommends bidirectional endoscopy over no endoscopy in patients with iron deficiency anemia 2
• Colonoscopy has a diagnostic accuracy of 72-86% in patients with lower gastrointestinal bleeding 3

Diagnostic Algorithm

1. Colonoscopy should be performed first, especially in patients older than 50 years or without symptoms indicating an upper GI source 4, 5

2. Upper endoscopy (EGD) should follow, even if colonoscopy identifies a potential bleeding source, as dual pathology is common 2

3. Small bowel biopsies should be taken during upper endoscopy to rule out celiac disease, which is present in 2-3% of patients with iron deficiency anemia 2

4. If both colonoscopy and upper endoscopy are negative:

   • Consider capsule endoscopy as the next step, which has a diagnostic yield of 61-74% in obscure GI bleeding 5
   • Testing for H. pylori should be performed, as treatment of H. pylori infection in conjunction with iron replacement has been shown to improve hemoglobin levels 2

Common Sources of Bleeding to Evaluate

• Colon: Colorectal cancer, large polyps (>2cm), angiodysplasia, diverticular disease 1, 6
• Upper GI tract: Peptic ulcer disease (gastric and duodenal ulcers), esophagitis, gastritis, vascular malformations 6
• Small bowel: Angiectasia (most common cause of obscure bleeding, accounting for up to 80% of cases), small bowel tumors (especially in patients <50 years) 2, 3

Treatment Approach

• Iron supplementation should be initiated to correct anemia and replenish body stores 2, 1
• Treatment should be directed at the identified source of bleeding 1
• Iron therapy should be continued for three months after correction of anemia to replenish iron stores 2
• Hemoglobin concentration and red cell indices should be monitored at three-month intervals for one year and then after a further year 1

Common Pitfalls to Avoid

• Do not rely solely on fecal occult blood testing without further evaluation, as it is insensitive and non-specific for determining the source of bleeding 2, 1
• Avoid accepting minor upper GI findings (such as erosions or mild esophagitis) as the sole cause of iron deficiency without completing lower GI evaluation 2
• Do not overlook the possibility of small bowel sources when both upper and lower endoscopies are negative 3
• Avoid missing subtle lesions during endoscopy by using techniques such as cap-fitted endoscopy to examine blind areas 3

Special Considerations

• In patients younger than 50 years, small bowel tumors are the most common cause of obscure bleeding, making aggressive investigation particularly important in this population 3
• For patients with ongoing or recurrent bleeding after initial treatment, repeat endoscopic examinations can be worthwhile 3
• If iron deficiency anemia persists or recurs despite treatment of identified lesions, further investigation may be necessary 2