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Examination of the blood cell counts and their appearance on a blood film is central to the diagnosis of blood cell diseases and can give important information about numerous other degenerative, inflammatory, and neoplastic diseases that are reflected in quantitative or qualitative changes of blood cells. Examples are the anemia accompanying chronic renal disease, chronic inflammation, or iron deficiency, the presence of malarial parasites in red cells, the eosinophilia of parasitic infection, the decrease in platelets resulting from immune thrombocytopenia, and other key findings on a blood examination that reflect numerous disease states. By careful examination of the blood, an experienced observer can diagnose all types of leukemia and closely related diseases. In few other disciplines can a physician make a specific diagnosis with easily accessible tissue samples and methods that can be used in a physician’s office. Today, blood examination is conducted almost exclusively in diagnostic laboratories, but the results can be provided to the clinician within a few hours of drawing the sample. Assessment of the concentration of red cells, reticulocytes, leukocytes, specific leukocyte types, and platelets; morphology of red cells, white cells, and platelets; identification of intracellular parasites, malignant cells, and marrow precursors (e.g., nucleated red cells) provides a large amount of information from the “complete blood count,” quickly and accurately.

Acronyms and Abbreviations

Acronyms and abbreviations that appear in the chapter include: CHr, reticulocyte-specific hemoglobin content; EDTA, ethylenediaminetetraacetic acid; fl, femtoliter; Hct, hematocrit; Ig, immunoglobulin; MCH, mean cell hemoglobin; MCHC, mean cell hemoglobin concentration; MCV, mean cell volume; MCVr, mean cell volume of reticulocytes; MPV, mean platelet volume; NHANES, National Health and Nutrition Examination Survey; NK, natural killer; PDW, platelet volume distribution width; RBC, red blood cell; RDW, red cell distribution width; RET-He, reticulocyte-specific hemoglobin content.

The blood is examined so as to answer these questions: Is the marrow producing appropriate numbers of mature cells in the major hematopoietic lineages? Is the development of each hematopoietic lineage qualitatively normal? Quantitative measures available from automated cell counters are reliable and provide a rapid and cost-effective way to screen for major disturbances of hematopoiesis or abnormalities that reflect nonhematopoietic diseases, such as inflammatory, degenerative, or neoplastic states. Light microscopic observation of the blood film is essential to confirm certain quantitative results and to investigate qualitatively abnormal differentiation of the hematopoietic lineages. Based on examination of the blood, the physician is directed toward a more focused assessment of marrow function or to systemic disorders that secondarily involve the hematopoietic system.

The complete blood count is a necessary part of the diagnostic evaluation in a broad variety of clinical conditions. Similarly, the leukocyte differential count and examination of the blood film, in spite of limitations as a screening test for occult disease,1 is important in initial consideration of the differential diagnosis in most ill patients. Although quantitative and morphologic examination of the cells of the blood are considered separately in this chapter, ...

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