Should a Cologuard or Fecal Occult Blood Test (FOBT) be done for a patient with iron deficiency anemia?

Should Cologuard or FOBT Be Performed in a 79-Year-Old with Iron Deficiency Anemia?

Neither Cologuard nor fecal occult blood testing should be performed in a 79-year-old patient with iron deficiency anemia—proceed directly to bidirectional endoscopy (colonoscopy and upper endoscopy) instead. 1, 2

Why Stool-Based Tests Are Not Appropriate

FIT/FOBT Is Explicitly Contraindicated in Iron Deficiency Anemia

• The 2023 APAGE-APSDE guidelines explicitly state: "We do not recommend the use of FIT in patients with iron deficiency anaemia." 1
• FIT demonstrates poor sensitivity (only 58%) and specificity (84%) in patients with iron deficiency anemia, making it unreliable for detecting the underlying gastrointestinal pathology. 1
• The British Society of Gastroenterology states that faecal occult blood testing is of no benefit in the investigation of iron deficiency anemia. 2
• The presence of iron deficiency anemia itself already indicates chronic gastrointestinal blood loss requiring direct visualization—stool tests add no diagnostic value and only delay appropriate investigation. 1, 2

Cologuard Has Similar Limitations

• While Cologuard (multi-target stool DNA) is not specifically addressed for iron deficiency anemia in the guidelines, it is designed as a screening test for average-risk populations, not as a diagnostic test for symptomatic patients. 1
• Like FIT, Cologuard would be inappropriate when iron deficiency anemia has already identified a high-risk situation requiring definitive evaluation. 1

The Correct Diagnostic Approach

Bidirectional Endoscopy Is the Standard of Care

• The AGA recommends bidirectional endoscopy (both esophagogastroduodenoscopy and colonoscopy) over no endoscopy for asymptomatic postmenopausal women and men with iron deficiency anemia. 1
• Both procedures should be performed at the same setting. 1
• Upper GI endoscopy reveals a cause in 30-50% of patients with iron deficiency anemia. 1
• Small bowel biopsies should be taken during upper endoscopy, as 2-3% of patients presenting with iron deficiency anemia have celiac disease. 1

Why Both Upper and Lower Endoscopy Are Necessary

• In elderly patients (like this 79-year-old), investigation of the colon is particularly productive, but upper GI evaluation remains mandatory. 1
• Dual pathology occurs in approximately 10-15% of cases—finding one lesion does not exclude another. 2
• Even when a lower GI source is identified, upper endoscopy should still be performed to rule out synchronous lesions. 3

Critical Pitfalls to Avoid

Do Not Use Intermediate Screening Steps

• Do not rely on FOBT or Cologuard as an intermediate step before endoscopy in patients with confirmed iron deficiency anemia. 2
• The presence or absence of gastrointestinal symptoms, positive fecal occult blood, and NSAID use are of limited value in guiding the diagnostic procedure and should not deter complete investigation. 3

Do Not Accept Incomplete Evaluation

• Do not accept minor upper GI findings (such as erosions or mild esophagitis) as the sole cause without completing lower GI evaluation. 2
• If both upper and lower endoscopies are negative, consider small bowel sources of bleeding. 2, 4

Age-Specific Considerations for This 79-Year-Old Patient

• In elderly patients with iron deficiency, colonoscopy frequently identifies colorectal cancer or polyps as the source. 1, 3
• The lower the hemoglobin level, the more likely there is serious underlying pathology and the more urgent the need for investigation. 2
• Age alone should not preclude thorough investigation, as elderly patients with iron deficiency have high rates of significant gastrointestinal lesions regardless of hemoglobin level. 3