What is the diagnosis and treatment for microcytic hypochromic anemia with high RDW and normal hemoglobin levels?

Microcytic Hypochromic Anemia with High RDW and Normal Hemoglobin

This presentation strongly suggests iron deficiency anemia (IDA), and you should immediately check serum ferritin to confirm the diagnosis before initiating iron supplementation. 1

Understanding the Laboratory Pattern

The combination of laboratory findings you describe creates a specific diagnostic signature:

• High RDW (>14.0%) with microcytosis (low MCV) is highly indicative of iron deficiency anemia 1
• The elevated RDW reflects anisocytosis—heterogeneous red cell populations with varying sizes as the body attempts to produce new cells with insufficient iron 2
• Normal hemoglobin does not exclude iron deficiency, as compensatory mechanisms (including the elevated RBC count you're seeing) may maintain hemoglobin levels despite depleted iron stores 1
• The low MCH and MCHC indicate hypochromia, confirming inadequate hemoglobin synthesis within the red cells 1

Why This is Iron Deficiency (Not Thalassemia)

The elevated RDW is the key discriminator here:

• Iron deficiency typically presents with RDW >14.0% due to heterogeneous microcytic cells at different stages of iron depletion 1, 2
• Thalassemia trait characteristically shows low or normal RDW (≤14.0%) because the microcytic cells are uniformly small and homogeneous 3
• While some thalassemia cases can have elevated RDW, the combination of high RDW with microcytosis makes iron deficiency far more likely 4, 2
• Studies show RDW is significantly higher in IDA compared to thalassemia (mean 20.20% vs 17.08%, p<0.001) 2

Essential Confirmatory Testing

Order these tests immediately to confirm iron deficiency:

• Serum ferritin (<12 μg/dL is diagnostic; <30 μg/L suggests iron deficiency in absence of inflammation; <100 μg/L with inflammation) 1
• Transferrin saturation (<30% supports iron deficiency) 1
• C-reactive protein (CRP) to assess for inflammation that might elevate ferritin falsely 3
• Consider serum iron (low) and total iron binding capacity (increased) as additional confirmatory tests 1

Critical Pitfall to Avoid

Never assume iron deficiency based solely on microcytosis—but in your case, the elevated RDW makes iron deficiency highly likely, not just possible. 3 However, you must still confirm with ferritin testing before treatment because:

• Combined deficiencies (iron plus B12 or folate) can create confusing patterns 3, 1
• Anemia of chronic disease can coexist with iron deficiency 1, 5
• Do not empirically treat with iron without confirming iron deficiency, as this can cause iron overload in thalassemia patients 3

Investigating the Underlying Cause

Once iron deficiency is confirmed, you must identify the source:

In adult men and post-menopausal women:

• Gastrointestinal blood loss is the most common cause 1
• Perform both upper and lower endoscopy to exclude malignancy—this is mandatory regardless of symptom severity 3, 1
• Common GI causes include colonic cancer/polyps, NSAID use, gastric cancer, angiodysplasia, and inflammatory bowel disease 1

In pre-menopausal women:

• Menstrual blood loss is the most common cause 1
• Still investigate for GI sources if menstrual losses seem inadequate to explain the deficiency 1

In all patients:

• Screen for celiac disease (malabsorption) 1
• Assess dietary iron intake 1

Treatment Approach

Once iron deficiency is confirmed:

1. Oral iron supplementation is first-line treatment 1, 5
2. A therapeutic response to three weeks of oral iron confirms the diagnosis 1
3. Continue iron therapy for 3-6 months after normalization of hemoglobin to replenish iron stores 1
4. Monitor hemoglobin, MCV, and RDW to assess response 1

Consider intravenous iron if:

• Malabsorption is present 1
• Intolerance to oral iron occurs 1
• Inflammatory bowel disease or other inflammatory conditions exist (higher doses needed) 1

If no response after 4 weeks:

• Reassess diagnosis and adherence 1
• Consider combined deficiencies 1
• Re-evaluate for ongoing blood loss 1