Red Cell Indices

Mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC) were first introduced by Wintrobe in 1929 to define the size (MCV) and hemoglobin content (MCH, MCHC) of red blood cells. Termed , these values are useful in elucidating the etiology of anemias. Red cell indices can be calculated if the values of hemoglobin, hematocrit (packed cell volume), and red blood cell count are known. With the general availability of electronic cell counters, red cell indices are now automatically measured in all blood count determinations. Variation in the size of red cells (anisocytosis) can be quantified and expressed as red cell distribution width (RDW) or as red cell morphology index. The RDW is more widely available and is discussed in this chapter. The size distribution of a population of cells is graphically represented by the red cell histograms (Price–Jones curves) (see Figure 152.1). Similar histograms are also available for white blood cells and platelets. MCV defines the size of the red blood cells and is expressed as femtoliters (10; fl) or as cubic microns (μm). The normal values for MCV are 87 ± 7 fl. MCH quantifies the amount of hemoglobin per red blood cell. The normal values for MCH are 29 ± 2 picograms (pg) per cell. MCHC indicates the amount of hemoglobin per unit volume. In contrast to MCH, MCHC correlates the hemoglobin content with the volume of the cell. It is expressed as g/dl of red blood cells or as a percentage value. The normal values for MCHC are 34 ± 2 g/dl. RDW represents the coefficient of variation of the red blood cell volume distribution (size) and is expressed as a percentage. The normal value for RDW is 13 ± 1.5%.