What does a CBC showing microcytic anemia with low MCH (Mean Corpuscular Hemoglobin) and MCHC (Mean Corpuscular Hemoglobin Concentration) and high RDW (Red Cell Distribution Width) indicate?

CBC Interpretation: Microcytic Anemia with Iron Deficiency

The CBC values showing low MCH (25.1 pg), low MCHC (30.2 g/dL), and high RDW (15.7%) strongly indicate iron deficiency anemia, which requires further workup to determine the underlying cause and appropriate iron replacement therapy.

Understanding the CBC Parameters

These CBC parameters reveal important information about the red blood cells:

• MCH (Mean Corpuscular Hemoglobin): 25.1 pg (normal: 26.6-33.0 pg)

  • Measures the average amount of hemoglobin per red blood cell
  • Low value indicates decreased hemoglobin content in each cell

• MCHC (Mean Corpuscular Hemoglobin Concentration): 30.2 g/dL (normal: 31.5-35.7 g/dL)

  • Measures the average concentration of hemoglobin in a given volume of red cells
  • Low value indicates hypochromia (pale red cells)

• RDW (Red Cell Distribution Width): 15.7% (normal: 11.7-15.4%)

  • Measures variation in red blood cell size
  • Elevated value indicates greater heterogeneity in cell size (anisocytosis)

Diagnostic Significance

This combination of laboratory findings is highly suggestive of iron deficiency anemia 1:

1. Low MCH and MCHC indicate reduced hemoglobin synthesis, characteristic of iron deficiency
2. Elevated RDW is a sensitive marker for iron deficiency, showing increased variation in red cell size 1

The pattern of low MCH/MCHC with high RDW helps distinguish iron deficiency from other causes of microcytic anemia:

• In iron deficiency: RDW is typically elevated (>14.0%) with low MCV 1
• In thalassemia minor: RDW is often normal with low MCV 1

Next Steps in Evaluation

Further workup should include:

1. Complete iron studies:

   • Serum ferritin (most powerful test for iron deficiency) 1
   • Transferrin saturation (TSAT)
   • Serum iron and total iron-binding capacity

2. Additional laboratory tests to rule out other causes:

   • Complete blood count with MCV (if not already done)
   • Reticulocyte count
   • CRP (to assess inflammation) 1
   • Consider vitamin B12 and folate levels if mixed deficiency suspected 1

3. Evaluate for underlying causes:

   • Gastrointestinal blood loss (most common cause in men and post-menopausal women) 1
   • Menstrual blood loss in pre-menopausal women
   • Malabsorption (e.g., celiac disease)
   • Poor dietary intake
   • Inflammatory bowel disease 1

Important Considerations

• Serum ferritin interpretation depends on inflammation status:

  • <30 μg/L indicates iron deficiency in the absence of inflammation 1
  • Up to 100 μg/L may still be consistent with iron deficiency if inflammation is present 1

• If both iron deficiency and chronic disease are present (ferritin 30-100 μg/L and low transferrin saturation), this represents a mixed picture 1

• Gastrointestinal evaluation is warranted in adult men and post-menopausal women with confirmed iron deficiency anemia to rule out occult GI bleeding from conditions like colorectal cancer 1

Treatment Approach

Once iron deficiency is confirmed:

1. Oral iron supplementation is first-line therapy for most patients

   • Typically ferrous sulfate, ferrous gluconate, or ferrous fumarate
   • Continue for 3-6 months after hemoglobin normalizes to replenish iron stores

2. Intravenous iron may be necessary if:

   • Oral iron is not tolerated
   • Malabsorption is present
   • Rapid repletion is needed
   • Ongoing blood loss exceeds oral replacement capacity

3. Address the underlying cause to prevent recurrence

The combination of low MCH, low MCHC, and high RDW is a classic pattern of iron deficiency anemia that requires prompt evaluation and treatment to improve patient outcomes.