Table 3.

Integrated Interpretation of Anemia Using MCV and RDW.

MCV	RDW	Typical interpretation	Key differential diagnoses	Practical clinical clues
Low (<80 fL)	Normal	Uniform microcytosis	Thalassemia trait, some anemia of chronic disease	RBC count often relatively preserved; mild anemia
Low (<80 fL)	High	Heterogeneous microcytosis	Iron deficiency anemia, sideroblastic anemia, combined disorders	Check ferritin and transferrin saturation; mixed populations common
Normal (80–100 fL)	Normal	Homogeneous normocytosis	Anemia of chronic disease, early anemia, renal anemia	Reticulocyte count critical for interpretation
Normal (80–100 fL)	High	Mixed cell population	Early iron deficiency, combined deficiency (iron + B12/folate), post-transfusion, recovery from anemia	RDW elevation may precede MCV change
High (>100 fL)	Normal	Uniform macrocytosis	Alcohol use, liver disease, hypothyroidism, some medications	Often stable, non-megaloblastic pattern
High (>100 fL)	High	Heterogeneous macrocytosis	Vitamin B12 deficiency, folate deficiency, myelodysplastic syndromes	Consider ineffective erythropoiesis and mixed populations

B12: vitamin B12; MCV: mean corpuscular volume; RBC: red blood cell; RDW: red cell distribution width.

Footnotes:

1. RDW reflects variability in red blood cell size (anisocytosis) and is particularly useful for detecting mixed cell populations or dynamic changes in erythropoiesis.

2. MCV should not be interpreted in isolation, as it may appear normal in the presence of mixed microcytic and macrocytic populations.

3. Reticulocyte count is essential for distinguishing between impaired production and increased destruction or loss.

4. MCV values may vary according to age and sex (see Figure 1); therefore, borderline values should be interpreted with caution.