What is the initial step to investigate a new onset anemia (low hemoglobin) in a 60-year-old patient with Crohn's disease?

Initial Investigation of Anemia in a 60-Year-Old with Crohn's Disease

The initial step to investigate a new hemoglobin drop to 105 g/L in a 60-year-old patient with Crohn's disease should be a complete blood count with iron studies, including serum ferritin and transferrin saturation. 1, 2

Comprehensive Evaluation Algorithm

Step 1: Laboratory Assessment

• Complete blood count with peripheral smear
• Reticulocyte count
• Iron studies:
  • Serum ferritin
  • Transferrin saturation
  • Serum iron
• Inflammatory markers (CRP, ESR)
• Vitamin B12 and folate levels

Step 2: Interpret Iron Studies in Context of Inflammation

• In Crohn's disease patients with active inflammation:
  • Iron deficiency is likely if ferritin is 30-100 μg/L with transferrin saturation <16% 1, 2
  • Anemia of chronic disease is likely if ferritin >100 μg/L and transferrin saturation <16% 2
  • Absolute iron deficiency is indicated by ferritin <30 μg/L regardless of inflammation 2

Step 3: Gastrointestinal Evaluation

• If iron deficiency is confirmed, proceed with GI investigations:
  • Upper GI endoscopy with duodenal biopsies (to rule out celiac disease, which occurs in 2-3% of patients with iron deficiency anemia) 1
  • Colonoscopy (even if upper GI findings suggest a cause, as dual pathology occurs in 10-15% of cases) 1

Important Considerations in Crohn's Disease

Anemia in Crohn's disease is typically multifactorial, with the most common causes being:

1. Iron deficiency due to:

   • Chronic GI blood loss
   • Reduced iron absorption (especially with ileal involvement)
   • Reduced oral intake

2. Anemia of chronic inflammation:

   • Inflammatory cytokines interfere with iron utilization
   • Hepcidin dysregulation impairs iron absorption and mobilization

3. Less common causes:

   • Vitamin B12 deficiency (particularly with ileal disease/resection)
   • Folate deficiency
   • Drug-induced myelosuppression (from medications used to treat Crohn's)
   • Hemolysis (rare autoimmune hemolytic anemia) 3

Common Pitfalls to Avoid

1. Accepting anemia as "normal" in Crohn's disease - Anemia significantly impacts quality of life and should always be thoroughly investigated 4

2. Misinterpreting ferritin levels - Standard cutoffs for iron deficiency don't apply in inflammatory states; ferritin up to 100 μg/L may still represent iron deficiency in active Crohn's disease 1, 2

3. Incomplete GI evaluation - Even with known Crohn's disease, new-onset anemia warrants endoscopic evaluation to rule out other causes, including malignancy 1

4. Focusing only on the GI tract - While GI blood loss is common, consider other causes like medication effects or nutritional deficiencies 1

5. Stopping investigation after finding one abnormality - Multiple causes of anemia often coexist in Crohn's disease patients 5, 4

By following this systematic approach to investigating anemia in a patient with Crohn's disease, you can identify the underlying cause(s) and implement appropriate treatment to improve both hemoglobin levels and quality of life.