3, 4 The Hgb is computed by a spectrophotometer after RBCs are lysed in a given volume of blood and the Hgb is chemically converted into a stable pigment. Both provide equivalent information, approximately conveyed by the RBC count, and are interchangeable. Two other “measured variables” of the complete blood cell count (CBC) are hemoglobin (Hgb) and hematocrit (Hct). Modern electronic counters are also capable of multimodal assessment of cell size and content, thus providing additional information about the various categories of WBCs including neutrophils, lymphocytes, monocytes, eosinophils, and basophils (ie, 5-part differential). In the context of RBCs, for example, these measurements are referred to as the mean corpuscular volume (MCV) and the RBC distribution width, respectively. Therefore, the electronic counter not only registers the total cell count but also estimates the average cell volume and the variation in cell size. Each electrical pulse represents an individual cell, and the pulse height indicates the cell volume. 1, 2 One such instrument, the Coulter counter, generates an electrical pulse when a blood cell passes through a small aperture surrounded by electrodes. Circulating blood cells, including red blood cells (RBCs), white blood cells (WBCs), and platelets, are counted and sized electronically by modern instruments.
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