Evaluation of microcytosis using serum ferritin and red blood cell distribution width.

Out of 104 patients with microcytosis (MCV less than 80 fl), 69% had an iron deficiency, 21% a chronic disease and 10% hemoglobinopathy or thalassemia trait. The absence of bone marrow iron stores or the response to iron supplementation were used to establish the diagnosis iron deficiency. On the basis of sensitivity (90%) and specificity (100%), the serum ferritin concentration is more suitable for assessment of iron deficiency than the serum iron concentration, the total iron-binding capacity or the percentual saturation of transferrin. The red cell distribution width (RDW) is the parameter with the highest sensitivity for iron deficiency (94%). An RDW value within the reference interval can be used to exclude iron deficiency in those cases in which the serum ferritin concentration does not accurately reflect the iron stores owing to severe tissue damage, as in inflammation or malignancy.