EPO and congenital thrombotic thrombocytopenic purpura: RDW is a parameter that reflects the heterogeneity of peripheral red blood cell volume and is considered to be a systemic inflammatory marker of in many chronic inflammation.12 As a low‐cost test, it is usually reported in the complete blood counts.13 Elevation of RDW may occur in ineffective red blood cell formation (iron deficiency, B12 or folate deficiency, and hemoglobinopathy), microangiopathic hemolytic anemias, increased red blood cell destruction (hemolysis) or post‐transfusion.14, 15 Pro‐inflammatory cytokines can inhibit erythropoietin‐induced erythrocyte maturation.