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COMPLETE BLOOD COUNT

LEARNING OBJECTIVE: Identify the five parts of a complete blood count, and recognize the testing procedures for the following: Unopette(r) Red Blood Cell Count, Microhematocrit, Unopette White Blood Cell Count, and Differential White Blood Cell Count.

A complete blood count consists of the following five tests:

Total red blood cell (RBC) count
Hemoglobin determination
Hematocrit reading
Total white blood cell (WBC) count
Differential white blood cell count
The complete blood count, commonly referred to as a CBC, is used in the diagnosis of many diseases. Blood collected for these tests are capillary or peripheral blood and venous blood. CBCs may be performed either manually or by using automated hematology analyzers. The manual method is used in isolated locations and on board some naval vessels where a hematology analyzer installation is not practical. For this reason, and because machines break down on occasion, the manual method will be covered in the following sections.

COUNTING BLOOD CELLS
To manually count red blood cells (erythrocytes) and white blood cells (leukocytes), you will need a microscope and an instrument called a hemacytometer. See figure 7-6. The hemacytometer is a thick glass slide with three raised parallel platforms on the middle third of the device. The central platform is subdivided by a transverse groove to form two halves, each wider than the two lateral platforms and separated from them and from each other by moats. The central platforms each contain a counting chamber and are exactly 0.1 mm lower than the lateral platforms.

Each counting chamber has precisely ruled lines etched into the glass, forming a grid. This grid or ruled area is so small that it can only be seen with the aid of a microscope. The grid used by most laboratories is the Improved Neubauer Ruling. See figure 7-7 for an example of the Improved Neubauer Ruling. The Improved Neubauer Ruling is 3 by 3 mm (9 mm 2 ) and subdivided into nine secondary squares, each 1 by 1 mm (1 mm 2 ).

A thick cover glass, ground to a perfect plane, accompanies the counting chamber (fig. 7-6). Ordinary cover glasses have uneven surfaces and should not be used. When the cover glass is in place on the platform of the counting chamber, there is a space exactly 0.1 mmthick between it and the ruled platform.

Counts of red blood cells and white blood cells are each expressed as concentration: cells per unit volume of blood. The unit of volume for cell counts is expressed as cubic millimeters (mm 3 ) because of the linear dimensions of the hemacytometer chamber.

TOTAL RED BLOOD CELL COUNT
The total red blood cell (erythrocyte) count is the number of red cells in one cubic millimeter of blood. The normal red blood cell count is as follows:


Figure 7-6.-Top and side views of a hemacytometer.

As we said earlier, the red cell count is used in the diagnosis of many diseases. For example, a red cell count that drops below normal values may indicate anemia and leukemia. On the other hand, a red cell count that rises above the normal values may indicate dehydration.

The Unopette(r) Method is used to manually count red blood cells. Material requirements and the step-by-step procedures for performing this procedure are provided in the following sections.



 


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