What are the main classifications of anemia?

Main Classifications of Anemia

Anemia can be most effectively classified using a combination of mean corpuscular volume (MCV) and reticulocyte count, which provides crucial information about both the type of anemia and the bone marrow's response to it. 1

Classification Based on MCV

Anemia is primarily categorized by red blood cell size:

1. Microcytic Anemia (MCV < 80 fL)

• Iron deficiency anemia - most common cause of microcytic anemia 1
• Anemia of chronic disease (cancer, infection, inflammatory conditions) 1
• Lead poisoning (rare) 1
• Hereditary microcytic anemia (thalassemia, sideroblastic anemia) 1, 2

2. Normocytic Anemia (MCV 80-100 fL)

• Acute hemorrhage - may initially show elevated reticulocytes 1
• Renal anemia - characterized by inappropriately low erythropoietin levels 1
• Anemia of chronic disease/inflammation 1, 3
• Bone marrow failure (aplastic anemia, pure red cell aplasia) 1, 2
• Primary bone marrow diseases (leukemias, myelodysplastic syndrome) 1
• Bone marrow infiltration by cancer (prostate, breast) 1

3. Macrocytic Anemia (MCV > 100 fL)

• Vitamin B12 deficiency (pernicious anemia, H. pylori gastritis, veganism) 1, 4
• Folate deficiency (increased requirements in pregnancy, hemolysis) 1, 4
• Myelodysplastic syndrome 1, 5
• Medication-induced (hydroxyurea, methotrexate, azathioprine) 1, 4
• Alcoholism 1, 5
• Hypothyroidism 1, 4

Classification Based on Reticulocyte Count

The reticulocyte count provides critical information about bone marrow response:

1. Low/Normal Reticulocyte Count (Decreased Production)

• Indicates impaired bone marrow production of red blood cells 1, 6
• Common in nutritional deficiencies, bone marrow failure, and chronic disease 1

2. High Reticulocyte Count (Increased Destruction/Loss)

• Indicates normal or increased bone marrow production with peripheral destruction or loss 1, 6
• Common in hemolysis and acute blood loss 1

Combined Classification Approach

The most effective diagnostic approach combines both MCV and reticulocyte count:

Microcytic Anemia with Low/Normal Reticulocytes

• Iron deficiency, anemia of chronic disease, lead poisoning, hereditary anemias 1

Microcytic Anemia with High Reticulocytes

• Hemoglobinopathies (thalassemia) 1

Normocytic Anemia with Low/Normal Reticulocytes

• Acute hemorrhage, renal anemia, anemia of chronic disease, bone marrow failure 1

Normocytic Anemia with High Reticulocytes

• Hemolytic anemia 1, 2

Macrocytic Anemia with Low/Normal Reticulocytes

• Vitamin B12/folate deficiency, MDS, medication effects, hypothyroidism 1, 4

Macrocytic Anemia with High Reticulocytes

• Hemolysis (false macrocytosis), MDS with hemolysis 1

Important Clinical Considerations

• Overlapping presentations: Mixed deficiency states can neutralize MCV abnormalities, resulting in a normal MCV despite underlying pathology 1, 7
• Red cell distribution width (RDW): A high RDW can help identify iron deficiency when microcytosis and macrocytosis coexist 1, 6
• Inflammation impact: In inflammatory conditions, ferritin levels may be elevated despite iron deficiency, potentially masking concurrent iron deficiency 1, 4
• Diagnostic limitations: Recent research suggests that MCV-guided classification alone may lead to incorrect exclusion of certain anemia etiologies; broader laboratory testing is recommended 7

Initial Diagnostic Workup

Minimum initial workup should include:

• Complete blood count with MCV
• Reticulocyte count
• Serum ferritin
• Transferrin saturation
• C-reactive protein 1, 6

Additional testing based on initial results may include vitamin B12, folate, haptoglobin, LDH, bilirubin, and bone marrow examination 1, 4