What is the interpretation of a CBC showing microcytic anemia with normal hemoglobin and hematocrit levels, and an elevated RDW?

CBC Interpretation: Iron Deficiency Anemia

This CBC shows early iron deficiency anemia with normal hemoglobin but abnormal red cell indices, specifically elevated RDW, low MCH, and low MCHC, consistent with iron deficiency despite preserved hemoglobin levels.

Key Findings in the CBC

• RBC: 5.35 H (elevated)
• Hemoglobin: 13.9 (normal)
• Hematocrit: 45.7 (normal)
• MCV: 85 (normal)
• MCH: 26.0 L (decreased)
• MCHC: 30.4 L (decreased)
• RDW: 16.4 H (elevated)

Interpretation and Diagnosis

Pattern Analysis

This pattern represents early or developing iron deficiency anemia where:

• The elevated RDW (16.4%) indicates increased variability in red cell size, a hallmark of early iron deficiency 1
• Low MCH and MCHC values indicate hypochromia (reduced hemoglobin content in red cells)
• Normal MCV with low MCH suggests early microcytic changes where some cells are becoming smaller while others remain normal sized
• Elevated RBC count represents a compensatory mechanism to maintain normal hemoglobin levels

Differential Diagnosis

1. Iron Deficiency Anemia (most likely): The combination of elevated RDW with low MCH and MCHC is highly suggestive of iron deficiency 1

2. Thalassemia trait: Less likely because:

   • RDW is typically normal or only mildly elevated in thalassemia trait
   • The RDW >14.0% with low MCH strongly favors iron deficiency over thalassemia 1

3. Combined iron deficiency and thalassemia: Possible but less common

4. Anemia of chronic disease: Less likely with this pattern of indices

Next Steps in Evaluation

1. Iron studies to confirm diagnosis:

   • Serum ferritin (will be <30 μg/L in uncomplicated iron deficiency) 1
   • Transferrin saturation (will be <16% in iron deficiency) 1
   • Serum iron and total iron binding capacity

2. Evaluate for causes of iron deficiency:

   • Occult blood loss (stool guaiac testing)
   • Menstrual blood loss assessment in females
   • Gastrointestinal evaluation if indicated (endoscopy)
   • Dietary assessment for iron intake

Management Recommendations

1. Oral iron supplementation is the first-line treatment:

   • Ferrous sulfate 325 mg (65 mg elemental iron) 1-3 times daily
   • Take on empty stomach with vitamin C to enhance absorption
   • Continue for 3-6 months to replenish iron stores even after hemoglobin normalizes 1

2. Follow-up testing after 4-8 weeks of therapy:

   • Expect improvement in RDW, MCH, and MCHC
   • Hemoglobin may increase if it decreases from current normal level

3. Dietary counseling to increase iron intake:

   • Red meat, poultry, fish
   • Beans, lentils, spinach
   • Iron-fortified foods

Clinical Pearls and Pitfalls

• Early iron deficiency can present with normal hemoglobin and MCV but abnormal RDW, MCH and MCHC
• RDW >14.0% with microcytic or normocytic indices is highly suggestive of iron deficiency 1, 2
• Elevated RBC count is a compensatory mechanism to maintain normal hemoglobin despite reduced hemoglobin content per cell
• Normal hemoglobin does not rule out iron deficiency; red cell indices may be abnormal before anemia develops
• Treatment should continue for several months after normalization of hemoglobin to replenish iron stores

This pattern represents early iron deficiency that should be addressed before it progresses to frank anemia with reduced hemoglobin levels.