Definition of Normocytic Anemia
Normocytic anemia is defined as anemia with a mean corpuscular volume (MCV) of 80-100 fL, indicating red blood cells of normal size despite reduced hemoglobin concentration. 1
Morphologic Classification
Normocytic anemia represents one of three morphologic categories used to classify anemia based on red blood cell size:
- Microcytic anemia: MCV < 80 fL (typically iron deficiency, thalassemia) 1
- Normocytic anemia: MCV 80-100 fL 1, 2
- Macrocytic anemia: MCV > 100 fL (typically B12/folate deficiency) 1
Common Causes
The major etiologies of normocytic anemia include:
- Hemorrhage (acute blood loss) 1, 3
- Hemolysis (destruction of red blood cells) 1, 2
- Bone marrow failure (aplastic anemia, malignancy infiltration) 1, 3
- Anemia of chronic inflammation/disease (most common normocytic anemia) 1, 3
- Renal insufficiency (erythropoietin deficiency) 1, 3
Critical Diagnostic Approach
The reticulocyte count (corrected for degree of anemia) is the key follow-up test that distinguishes between production defects versus destruction/loss mechanisms. 1
Reticulocyte Index Interpretation:
- Low reticulocyte index (<1.0-2.0): Indicates decreased RBC production, suggesting bone marrow dysfunction, aplastic anemia, or cancer-related therapy effects 1
- High reticulocyte index (>2.0): Indicates normal or increased RBC production, suggesting ongoing blood loss or hemolysis 1, 2
Important Clinical Pitfall
Mixed deficiencies (such as combined iron and B12 deficiency) can neutralize MCV changes, presenting as normocytic anemia when both microcytic and macrocytic processes coexist. 3 An elevated red cell distribution width (RDW >15%) serves as a critical clue to this dual pathology. 3
Characteristics in Chronic Kidney Disease
In chronic renal failure, normochromic normocytic anemia typically develops when glomerular filtration rate drops below 20-30 mL/min, primarily due to inadequate erythropoietin production relative to the falling hemoglobin. 4