What labs to order for a male with iron deficiency anemia (IDA) secondary to gastrointestinal bleeding, with negative Esophagogastroduodenoscopy (EGD) and colonoscopy results?

Laboratory Evaluation for Males with Iron Deficiency Anemia and Negative Bidirectional Endoscopy

For males with iron deficiency anemia secondary to gastrointestinal bleeding who have negative EGD and colonoscopy results, capsule endoscopy is strongly recommended as the next diagnostic step to identify small bowel sources of bleeding.

Initial Laboratory Assessment

• Complete iron studies including:

  • Serum ferritin (most powerful test for iron deficiency)
  • Transferrin saturation (helpful if false-normal ferritin is suspected)
  • Serum iron
  • Total iron binding capacity (TIBC)

• Complete blood count (CBC) with differential to assess severity of anemia and red cell indices

• Celiac disease screening:

  • Tissue transglutaminase antibody (IgA type)
  • Total IgA level (to ensure validity of tTG-IgA)

• Urinalysis to exclude renal sources of blood loss

Small Bowel Evaluation

After negative EGD and colonoscopy, small bowel evaluation is essential as the British Society of Gastroenterology strongly recommends 1:

1. Capsule endoscopy is the preferred first-line test for examining the small bowel in IDA because:

   • Highly sensitive for mucosal lesions
   • Diagnostic yield of 50-73% in patients with IDA and negative bidirectional endoscopy 2
   • Particularly valuable in older adults, where diagnostic yield increases with age

2. CT/MR enterography if capsule endoscopy is contraindicated or unavailable:

   • Complementary to capsule endoscopy for inflammatory and neoplastic disease
   • Better for extraluminal pathology

Additional Testing to Consider

• H. pylori testing if not previously done, as eradication may help resolve recurrent IDA 1

• Repeat quality assessment of previous endoscopic procedures:

  • Ensure adequate visualization of all segments
  • Consider repeat procedures if quality was suboptimal

• Device-assisted enteroscopy (if capsule endoscopy identifies lesions requiring biopsy or therapy) 1

Common Causes of Small Bowel Bleeding in Males

• Vascular lesions (angioectasias) - most common in patients >40 years old
• Small bowel tumors - more common in patients <50 years old
• NSAID-induced enteropathy
• Crohn's disease
• Dieulafoy's lesion

Management Approach

1. Start iron replacement therapy immediately while investigations are ongoing 1:

   • One tablet daily of ferrous sulfate, fumarate, or gluconate
   • Monitor hemoglobin response within 4 weeks
   • Continue for 3 months after normalization to replenish iron stores

2. Proceed with capsule endoscopy as soon as possible 1

3. If capsule endoscopy is negative but IDA persists or recurs:

   • Consider repeat capsule endoscopy
   • Evaluate renal tract even if initial urinalysis was negative 3

4. For persistent unexplained IDA despite thorough investigation:

   • Long-term iron replacement therapy is appropriate 1
   • Periodic monitoring (every 3-6 months initially)

Important Considerations

• Males with IDA have a higher risk of gastrointestinal malignancy, warranting thorough investigation 3

• A good response to iron therapy (Hb rise ≥10 g/L within 2 weeks) suggests absolute iron deficiency, even with equivocal iron studies 1

• Small bowel lesions may be missed on initial capsule endoscopy, so close follow-up is essential 1

• Capsule endoscopy has a higher diagnostic yield when performed as soon as possible after a bleeding episode 1

By following this systematic approach to laboratory evaluation and small bowel assessment, the source of gastrointestinal bleeding can be identified in the majority of males with iron deficiency anemia and negative bidirectional endoscopy.