What is the management approach for a patient with a positive fecal occult blood test (FOBT), low hemoglobin (hgb), and no active bleeding noted?

Management of Positive Fecal Occult Blood Test with Low Hemoglobin and No Active Bleeding

A patient with a positive fecal occult blood test (FOBT) and low hemoglobin without active bleeding requires prompt endoscopic evaluation with colonoscopy as the first-line diagnostic procedure, followed by esophagogastroduodenoscopy (EGD) if no source is identified. 1

Initial Evaluation

• A positive FOBT indicates the presence of blood in stool, which may derive from colorectal cancer or large polyps (>2cm), necessitating a complete evaluation of the colon 1
• Low hemoglobin in combination with a positive FOBT strongly suggests occult gastrointestinal bleeding, which requires thorough investigation even in the absence of visible bleeding 2, 3
• Faecal occult blood testing alone is considered insensitive and non-specific for determining the source of bleeding, so further diagnostic workup is essential 1

Diagnostic Algorithm

First-Line Investigations:

1. Colonoscopy:

   • Preferred initial diagnostic procedure for positive FOBT as it allows direct visualization of the entire colon and removal of polyps 1, 4
   • Has higher sensitivity and specificity for detecting adenocarcinomas and polyps compared to other testing methods 1

2. If colonoscopy is negative or incomplete:

   • Proceed to upper GI evaluation with esophagogastroduodenoscopy (EGD) 1, 3
   • This approach is necessary as dual pathology (lesions in both upper and lower GI tracts) occurs in 10-15% of patients 1

Second-Line Investigations (if first-line is negative):

• Repeat endoscopies may be warranted as they can identify previously missed lesions in up to 35% of cases 3
• Capsule endoscopy should be considered for evaluating the small bowel if both EGD and colonoscopy are negative, with a diagnostic yield of 61-74% 5, 3
• CT enterography or deep enteroscopy may be needed for further investigation of small bowel lesions identified on capsule endoscopy 5, 3

Special Considerations

• Iron deficiency anemia: In men and postmenopausal women with iron deficiency anemia, gastrointestinal evaluation is nearly always indicated due to the risk of gastrointestinal malignancy 2, 6
• Pre-menopausal women: Consider gynecological causes of blood loss, but don't attribute iron deficiency anemia solely to menstruation without appropriate GI evaluation 1, 3
• Medication use: Do not attribute positive FOBT to low-dose aspirin or anticoagulant medications without further evaluation 3

Treatment Approach

• Iron supplementation: All patients should receive iron supplementation to correct anemia and replenish body stores 1

  • Typically ferrous sulfate 200mg three times daily
  • Continue for three months after correction of anemia to replenish iron stores

• Follow-up monitoring:

  • Monitor hemoglobin concentration and red cell indices at three-month intervals for one year and then after a further year 1
  • Additional oral iron should be given if hemoglobin or MCV falls below normal 1
  • Further investigation is only necessary if hemoglobin and MCV cannot be maintained with iron supplementation 1

Common Pitfalls

• Accepting minor upper GI findings (such as erosions or mild esophagitis) as the sole cause of iron deficiency without completing lower GI evaluation 1
• Relying on single-sample FOBT collected during digital rectal examination, which has poor sensitivity and may yield false positives 1
• Failing to consider obscure bleeding sources in the small bowel when both upper and lower endoscopies are negative 5, 7
• Overlooking commonly missed lesions such as angioectasias, Dieulafoy's lesion, and Cameron's erosions 5