ANSWER TO QUESTION # 02

Question#02

How is the RDW useful for distinguishing causes of microcytic anemia?

ANSWER:

The red blood cell distribution width (RDW) is a quantification of anisocytosis (variation in red-cell size). It is derived from the RBC size histogram that is measured by automated cell counters, and it is reported as a percentage. In children, normal values range from about 11.5% to 14.5% but can vary among instruments. Statistically, it is the coefficient of variation of red-cell volume distribution. When elevated in a patient with microcytosis, it suggests that iron deficiency is a more likely cause of anemia than the thalassemia trait. Children with the thalassemia trait tend to have values that overlap with normal RDW values. The combination of an RDW above the normal range with a free erythrocyte protoporphyrin level of >35 μg/dL is more sensitive and specific for iron-deficiency anemia.