How to manage a patient with microcytic anemia and elevated RDW?

Management of Microcytic Anemia with Elevated RDW

A patient with microcytic anemia (MCV 77) and markedly elevated RDW (56.3) should be thoroughly evaluated for iron deficiency anemia as the most likely diagnosis, with immediate initiation of iron supplementation and investigation for underlying gastrointestinal blood loss.

Diagnostic Interpretation of Lab Values

The laboratory values show:

• MCV 77 (below normal range, indicating microcytosis)
• MCH 24 (low, consistent with hypochromia)
• MCHC 31 (low-normal)
• RDW 56.3 (markedly elevated)
• RDW ratio 20.7 (elevated)

These findings strongly suggest iron deficiency anemia (IDA) for several reasons:

1. The combination of low MCV with markedly elevated RDW is highly characteristic of iron deficiency anemia 1.
2. According to guidelines, a low MCV with RDW >14% indicates iron deficiency anemia, whereas a low MCV with normal RDW would suggest thalassemia minor 1.
3. The extremely high RDW (56.3) indicates significant red cell size variation, which is typical in iron deficiency 1.

Diagnostic Algorithm

1. Confirm iron deficiency:

   • Measure serum ferritin (most powerful test for iron deficiency) 1
   • Check transferrin saturation (should be <30% in iron deficiency) 1
   • Consider additional tests: serum iron, total iron binding capacity 1

2. Rule out other causes of microcytic anemia:

   • Thalassemia (typically has normal RDW, though some cases may have elevated RDW) 1, 2
   • Anemia of chronic disease (check CRP/ESR for inflammation) 1
   • Sideroblastic anemia (rare) 1

3. Assess reticulocyte count:

   • Low or normal reticulocytes would confirm inadequate erythropoiesis consistent with iron deficiency 1

Treatment Plan

1. Iron supplementation:

   • Oral iron therapy is first-line treatment for most patients with iron deficiency anemia 1
   • Standard dosing: 100-200 mg elemental iron daily in divided doses
   • Monitor response: expect hemoglobin increase of at least 2 g/dL within 4 weeks 1

2. Consider IV iron if:

   • Oral iron is not tolerated
   • Patient has malabsorption
   • Anemia is severe or symptomatic
   • Patient has inflammatory bowel disease with active inflammation 1

3. Investigate underlying cause:

   • Gastrointestinal evaluation is mandatory in adult men and post-menopausal women with iron deficiency anemia 1
   • Upper endoscopy and colonoscopy to rule out GI malignancy
   • Consider small bowel evaluation if upper and lower endoscopies are negative
   • Test for celiac disease (common cause of iron malabsorption) 1
   • Assess for NSAID use (common cause of GI blood loss) 1

Special Considerations

• Caution: Do not assume thalassemia without appropriate testing, even in patients from high-risk ethnic groups 1
• Pitfall to avoid: Accepting iron deficiency as the diagnosis without investigating the underlying cause, particularly in men and post-menopausal women where GI malignancy must be excluded 1
• Important: The extremely high RDW (56.3) is unusual even for typical iron deficiency and may indicate severe, longstanding deficiency or possibly a combined deficiency (e.g., concurrent folate deficiency) 1

Follow-up

1. Repeat CBC after 4 weeks of iron therapy to document response
2. Continue iron therapy for 3-6 months after normalization of hemoglobin to replenish iron stores
3. If no response to oral iron after 4 weeks, consider:
   • Poor compliance
   • Ongoing blood loss exceeding iron replacement
   • Malabsorption
   • Incorrect diagnosis

The combination of microcytosis with markedly elevated RDW strongly points to iron deficiency anemia requiring prompt treatment and investigation of the underlying cause, particularly to exclude gastrointestinal malignancy in adult men and post-menopausal women 1.