The Complete Blood Count

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The complete blood count (CBC) is one of the most frequently ordered and most time-honored laboratory tests in the hematology laboratory. This evaluation consists of nine components and offers the clinician a variety of hematological data to interpret and review that directly relate to the health of the bone marrow, represented by the numbers and types of cells in the peripheral circulation. The nine components of the CBC (Fig. 2.6) are the white blood cell count (WBC), red blood cell count (RBC), Hgb, hematocrit (Hct), mean corpuscular volume (MCV), mean corpuscular Hgb (MCH), mean corpuscular Hgb content (MCHC), platelet count, and red cell distribution width (RDW). Depending on the type of automated instrumentation used, some of these parameters are directly read from the instrument and some are calculated. Generally, most automated instruments directly read the WBC, RBC, Hgb, and MCV The Hct is a calculated parameter. Correlation checks between the Hgb and Hct are a significant part of quality assurance for the CBC and are known as the "rule of three." The formulas for correlation checks/rule of three are as follows: Hgb x 3 = Hct ± 3 and RBC X 3 = Hgb. As a matter of practice, each operator of any automated instrumentation should be able to quickly and accurately establish a correlation check for each sample. Failure to fall within the correlation check is usually the first indicator of preanalytic error and may indicate corrective actions such as reviewing a peripheral smear, tracing the origin of the samples, or other investigation. Additionally, each instrument presents a pictorial representation of the hematological data registered as either a histogram or a scatterplot, and most now offer an automated reticulocyte count. This is discussed in the Procedure section. Table 2.3 presents normal values for a CBC from the adult, and Table 2.4 gives selected red cell values for the newborn. These data are also presented on the inside cover of this text.

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Figure 2.5 Sample bone marrow report.

2004), most physicians reported that the most preferred information was the Hgb, Hct, platelet count, and WBC. The MCV was generally viewed as important by primary care physicians. The RDW and automated reticulocyte count were used primarily by "newer" clinicians.

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