Understanding High RDW-CV: Causes and Clinical Implications

Red Cell Distribution Width–Coefficient of Variation (RDW-CV) quantifies anisocytosis (variation in red blood cell size). Elevated RDW-CV (>14.5%) signals heterogeneous RBC populations.

Major Causes

Microcytic Processes (Low MCV)

• Iron Deficiency: Most common cause. Impaired hemoglobin synthesis → small RBCs mixed with normal.
• Thalassemia Trait: Genetic hemoglobin synthesis defect → microcytosis.
• Sideroblastic Anemia: Defective heme synthesis.

Macrocytic Processes (High MCV)

• B12/Folate Deficiency: Impaired DNA synthesis → large RBCs (macro-ovalocytes).
• Liver Disease: Altered lipid membranes → target cells, macrocytosis.
• Hypothyroidism: Reduced erythropoiesis efficiency.
• Alcohol, Medications (chemo, hydroxyurea)

Mixed/Dimorphic Anemias

• Combined deficiencies (iron + B12)
• Post-transfusion
• Myelodysplastic syndromes
• Sickle cell disease

Clinical Approach

1. Correlate with MCV, reticulocyte count, peripheral smear
2. Iron studies, B12/folate, TSH, LFTs, hemoglobin electrophoresis as indicated
3. Bone marrow if unclear

Prognostic Value

High RDW predicts mortality in heart failure, critical illness, and cardiovascular disease independent of anemia.