What is the role of gastrointestinal evaluation, including gastroscopy (upper endoscopy) and colonoscopy, in identifying the cause of iron deficiency anemia?

Role of Gastrointestinal Evaluation in Iron Deficiency Anemia

Bidirectional endoscopy (both gastroscopy and colonoscopy) is strongly recommended for asymptomatic postmenopausal women and men with iron deficiency anemia, and conditionally recommended for premenopausal women, as this approach identifies gastrointestinal malignancies and other bleeding sources that directly impact mortality. 1

Diagnostic Approach by Patient Population

Postmenopausal Women and Men

• Perform bidirectional endoscopy (gastroscopy + colonoscopy) as the standard of care in all asymptomatic patients with confirmed iron deficiency anemia (ferritin <45 ng/mL). 1
• This is a strong recommendation with moderate quality evidence from the American Gastroenterological Association. 1
• Upper endoscopy identifies bleeding sources in 30-50% of patients, including gastric cancer, peptic ulcers, and erosive lesions. 1, 2
• Colonoscopy detects colon cancer in approximately 10-15% of patients with iron deficiency anemia, making it critical for mortality reduction. 3, 2
• Dual pathology (lesions in both upper and lower GI tracts) occurs in 10-15% of cases, necessitating complete evaluation even when an upper source is found. 1

Premenopausal Women

• Bidirectional endoscopy is conditionally recommended over iron replacement alone (conditional recommendation, moderate quality evidence). 1
• The decision should weigh the patient's age and presence of other plausible causes (menstrual blood loss) against the small but real risk of missing GI malignancy. 1
• Younger premenopausal women (<40 years) without alarm symptoms may reasonably defer endoscopy initially. 4

What Gastroscopy Should Include

Essential Components During Upper Endoscopy

• Obtain small bowel biopsies from the duodenum routinely, as celiac disease accounts for 2-5% of iron deficiency anemia cases, even in asymptomatic patients. 1, 3
• Perform celiac serology (tissue transglutaminase antibody with total IgA) first; proceed to small bowel biopsy only if serology is positive. 1
• Identify non-bleeding causes including atrophic gastritis (found in 19-27% of cases) and H. pylori gastritis. 3
• Document peptic ulcers, erosive esophagitis, hiatal hernia with linear erosions, and vascular ectasias. 1, 2

H. Pylori Testing

• Non-invasive testing for H. pylori is conditionally recommended, followed by treatment if positive (conditional recommendation, low quality evidence). 1
• H. pylori gastritis can cause iron deficiency through impaired absorption even without overt bleeding. 3

What Colonoscopy Should Detect

Key Findings

• Colon cancer is the most common malignant cause, detected in 10-15% of patients with iron deficiency anemia. 3, 2, 5
• Identify colonic polyps, vascular ectasias (angiodysplasia), and inflammatory bowel disease. 1, 3, 2
• Complete colonoscopy is essential; if colonoscopy cannot be completed, double-contrast barium enema is an acceptable alternative. 1

Critical Pitfalls to Avoid

Do Not Stop at Upper GI Findings

• Never accept esophagitis, erosions, or peptic ulcer as the sole cause without completing lower GI evaluation, as dual pathology is common. 1
• The exception is if gastroscopy reveals gastric cancer or confirmed celiac disease with positive serology and biopsy. 1

When Both Endoscopies Are Negative

• Initial iron supplementation is preferred over routine video capsule endoscopy in uncomplicated asymptomatic patients (conditional recommendation, very low quality evidence). 1
• Small bowel investigation (capsule endoscopy, CT/MRI enterography) should be reserved for patients with transfusion-dependent anemia, visible blood loss (melena), or red flag symptoms (weight loss, abdominal pain, elevated CRP). 1, 4
• Follow-up studies demonstrate this conservative approach is safe when dietary deficiency is corrected, NSAIDs stopped, and hemoglobin monitored. 1

Special Consideration for Anticoagulation

• Exercise caution in patients on anticoagulation or antiplatelet therapy with negative bidirectional endoscopy, as identifying small bowel pathology may change management decisions. 1
• These patients may warrant earlier capsule endoscopy despite negative initial evaluation. 1

Diagnostic Yield

Overall Detection Rates

• Gastrointestinal evaluation identifies a likely cause in 85% of patients with unexplained iron deficiency anemia. 3
• Bleeding-associated causes (cancers, ulcers, vascular lesions) account for 37% of cases. 3
• Non-bleeding causes (atrophic gastritis, celiac disease, H. pylori) account for 51% of cases. 3

Age and Gender Patterns

• Patients with non-bleeding causes are younger (median 56 vs 70 years) and more likely female (59% vs 30%). 3
• Older patients are more likely to have bleeding-associated lesions including malignancy. 3, 5

When Symptoms Are Present

• Direct initial evaluation to the symptomatic site, as site-specific symptoms have 86% positive predictive value for detecting lesions in the corresponding bowel segment. 2
• However, complete bidirectional evaluation remains necessary due to the frequency of dual pathology. 1, 2