The RDW is only available if it is included in the instrument menu. Although different manufacturers use slightly different methods of obtaining data the RDW is generally thought of as the coefficient of variation of red cell volume distribution. The RDW, coupled with the MCV, gives more relevant information than an individual index. There are varying opinions on the clinical value of red cell indices. They are used to morphologically classify anemias and to select additional tests to determine the cause of an anemia.
Indices also change in response to treatment of some anemias.
These include the platelet distribution width and average platelet volume. They have limited use, but do correlate to flags on the platelet histogram that indicate giant platelet or platelet clumps. Anisocytosis - variance in red cell size as determined by viewing the diameter of the cells on a stained peripheral blood smear. Anemia - A reduction in the oxygen carrying capacity of the blood. Almost always manifested by a decreased hemoglobin and frequently accompanied by a decreased hematocrit and red cell count.