Materials Required for the Differential Count Procedure

Hypersegmented Neutrophil.—A hyperseg- mented neutrophil is a mature neutrophil. The nucleus of a hypersegmented neutrophil is divided into six or more segments or lobes (fig. 7-17). EOSINOPHIL.—Eosinophils aid in detoxifi- cation. They also break down and remove protein material. The cytoplasm of an eosinophil contains numerous coarse, reddish-orange granules, which are lighter colored than the nucleus (fig. 7-17). BASOPHIL.—The function of basophilic cells is unknown. It is believed, however, that basophilic cells keep the blood from clotting in inflamed tissue. Scattered large, dark-blue granules that are darker than the nucleus, characterize the cell as a basophil (fig. 7-17). Granules may overlay the nucleus as well as the cytoplasm. LYMPHOCYTE.—The function of lymphocytes is also unknown, but it is believed that they produce antibodies and destroy the toxic products of protein metabolism. The cytoplasm of a lymphocyte is clear sky blue, scanty, with few unevenly distributed, azurophilic granules with a halo around them (fig. 7-17). The nucleus is generally round, oval, or slightly indented, and the chromatin (a network of fibers within the nucleus) is lumpy and condensed at the periphery. MONOCYTE.—The monocyte, the largest of the normal white blood cells, destroys bacteria, foreign particles, and protozoa. Its color resembles that of a lymphocyte, but its cytoplasm is a muddy gray-blue (fig. 7-17). The nucleus is lobulated, deeply indented or horseshoe-shaped, and has a relatively fine chromatin structure. Occasionally, the cytoplasm is more abundant than in the lymphocyte. Materials Required for the Differential Count Procedure To perform a differential count, the following materials are required: � Four plain glass microscope slides, clean and dry � Wright-Giemsa stain solution (follow manufacturer’s directions for use and storage) � Staining containers � Deionized or distilled water � Microscope with light source � Immersion oil � Blood cell counter Differential Count Procedure The procedure for the differential white cell count is done in 4 steps: Step 1: Making the blood smear Step 2: Staining the cells Step 3: Counting the cells Step 4: Reporting the count Each step of this procedure will be discussed in the following sections. MAKING THE BLOOD SMEAR.—The simplest way to count the different types of white cells is to spread them out on a glass slide. The preparation is called a blood smear. There are two methods of making a blood smear: the slide method (covered in this chapter) and the cover glass method. It is very important to make a good blood smear. If it is made poorly, the cells may be so distorted that it will be impossible to recognize them. You should make at least two smears for each patient, as the additional smear should be examined to verify any abnormal findings. To prepare a blood smear for a differential count, follow the steps below: 1. Using a capillary tube, collect anticoagulated blood from a venous blood sample. 2. Deposit a drop of blood from capillary tube onto a clean, grease-free slide. Then place the slide on a flat surface, blood side up. 3. Hold a second slide between your thumb and forefinger and place the edge at a 23-degree angle against the top of the slide that holds the drop of blood (see figure 7-18, view A). Back the second slide down until it touches the drop of blood. The blood will distribute itself along the edge of the slide in a formed angle (see figure 7-18, view B). 4. Push the second slide along the surface of the other slide, drawing the blood across the surface in a thin, even smear (see figure 7-18, view C). If this is done in a smooth, uniform manner, a gradual tapering effect (or “feathering”) of the blood will occur on the slide. This “feathering” of the blood is essential to the counting process and is the principal characteristic of a good blood smear (see figure 7-18, view D). When 7-21