What is the appropriate diagnosis and treatment for a patient with hypochromic microcytic anemia and elevated RDW?

Diagnosis and Treatment of Hypochromic Microcytic Anemia with Elevated RDW

The laboratory findings of low MCH, low MCHC, borderline low MCV, and elevated RDW strongly suggest iron deficiency anemia as the most likely diagnosis, which should be confirmed with serum ferritin testing and treated with oral iron supplementation. 1

Interpretation of Laboratory Values

• The patient's CBC shows:
  • Normal WBC count (8.9 x10³/μL)
  • Elevated RBC count (5.51 x10⁶/μL) - likely compensatory mechanism
  • Normal hemoglobin (13.1 g/dL)
  • Normal hematocrit (43.5%)
  • Borderline low MCV (79 fL) - at lower limit of normal
  • Low MCH (23.8 pg) - hypochromia
  • Low MCHC (30.1 g/dL) - hypochromia
  • Elevated RDW (17.0%) - anisocytosis
  • Normal platelet count (442 x10³/μL) 1

Diagnostic Significance

• The combination of hypochromia (low MCH and MCHC), borderline microcytosis (MCV at lower limit), and elevated RDW (>14.0%) is highly suggestive of iron deficiency anemia 1, 2
• An elevated RDW indicates increased variation in red cell size (anisocytosis), which is characteristic of iron deficiency anemia 1
• While thalassemia can also present with microcytosis and hypochromia, it typically has a normal or only mildly elevated RDW, whereas this patient's RDW is significantly elevated (17.0%) 2, 3

Confirmatory Testing Required

• Serum ferritin is the most sensitive and specific test to confirm iron deficiency:
  • Serum ferritin <12 μg/dL is diagnostic of iron deficiency
  • In the presence of inflammation, ferritin up to 100 μg/L may still be consistent with iron deficiency 1
• Additional recommended tests include:
  • Transferrin saturation (<30% supports iron deficiency)
  • Serum iron (low in iron deficiency)
  • Total iron binding capacity (increased in iron deficiency) 1, 2

Differential Diagnosis

• Iron deficiency anemia - most likely based on laboratory findings 1, 2
• Thalassemia trait - less likely due to significantly elevated RDW, but cannot be completely excluded 3, 4
• Combined deficiency (iron plus B12 or folate) - possible but less common 1
• Anemia of chronic disease - can present with microcytosis but typically has normal RDW 2

Treatment Approach

1. Confirm diagnosis with serum ferritin and other iron studies 1, 2
2. Initiate oral iron supplementation - first-line treatment for iron deficiency anemia 1
   • Typical dose: 3-6 mg/kg/day of elemental iron divided into 1-3 doses
   • Continue for 3-6 months after normalization of hemoglobin to replenish iron stores 1
3. Investigate underlying cause of iron deficiency:
   • In adults: GI blood loss (colonic cancer/polyps, NSAID use, gastric cancer)
   • In women: Menstrual blood loss
   • Consider malabsorption (celiac disease)
   • Evaluate dietary iron intake 1

Monitoring and Follow-up

• Monitor hemoglobin, MCV, and RDW to assess response to treatment 1
• A therapeutic response to three weeks of oral iron confirms the diagnosis of iron deficiency 1
• If no response after 4 weeks, reassess diagnosis and adherence 1
• Consider hemoglobin electrophoresis if response is inadequate to rule out thalassemia 3, 4

Pitfalls and Caveats

• Not all patients with iron deficiency have elevated RDW; approximately 20% may have normal RDW values 5, 6
• The sensitivity of RDW for diagnosing iron deficiency anemia has been reported as 81% with specificity of only 53.4% 7
• Combined deficiencies (iron plus B12 or folate) may mask typical findings 1
• Anemia of chronic disease can coexist with iron deficiency 1
• A normal hemoglobin does not exclude iron deficiency, as compensatory mechanisms may maintain hemoglobin levels despite depleted iron stores 1
• In patients with inflammatory conditions, higher doses of iron may be needed for treatment 1