Newer machines, capable of calculating RDW or red cell morphology index, mean platelet volume, absolute lymphocyte count, and differential white cell count ate now being used in many clinical laboratories. Most of the automated machines give the following values: white cell count, red cell count, platelet count, hemoglobin, hematocrit, MCV, MCH, and MCHC. Instruments like the Coulter S model employ the principle of electric impedance others, like the Hemalog System Analyzer, use optical methods in performing cell counts. Two types of automated machines are generally used. Most clinical laboratories now use automated machines to perform blood counts (commonly called CBC) that include red cell indices as part of the profile. Similar histograms are also available for white blood cells and platelets. The size distribution of a population of cells is graphically represented by the red cell histograms (Price–Jones curves) (see Figure 152.1). The RDW is more widely available and is discussed in this chapter. 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. With the general availability of electronic cell counters, red cell indices are now automatically measured in all blood count determinations. Red cell indices can be calculated if the values of hemoglobin, hematocrit (packed cell volume), and red blood cell count are known.

Termed red cell indices, these values are useful in elucidating the etiology of anemias. 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.

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