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LEARNING OBJECTIVES
Describe the general principles behind commonly performed hematology tests and their uses in the pediatric population.
Discuss the different components and cellular elements that are evaluated on examination of the peripheral blood smear and bone marrow.
List common hematologic conditions in pediatric patients and summarize their expected laboratory findings.
Compare and contrast commonly used laboratory methods for the diagnosis of hemoglobinopathies.
Describe the pathophysiology of common quantitative and qualitative hemoglobin disorders.
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Hematology is the study of blood and its components and encompasses blood cells, hematopoietic precursors in marrow, blood proteins, and mechanisms of coagulation. This chapter deals specifically with the laboratory techniques used in the diagnosis and monitoring of diseases related to the blood with an emphasis on issues specific to the pediatric population. Common hematologic conditions including their clinical presentation, pathophysiology, and laboratory findings are addressed in this chapter. The function of platelets and proteins involved in blood coagulation are described in Chapter 16. Pediatric hematologic malignancies are beyond the scope of this chapter.
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HEMATOLOGY PRINCIPLES AND METHODS
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The complete blood count (CBC) is performed on whole blood collected in a purple top tube containing ethylenediaminetetraacetic acid (EDTA). The cellular components of blood include red blood cells, white blood cells and platelets and the components of a CBC include red blood cell measurements, white blood cell measurements, platelet measurements, and description of red blood cell morphology. Red blood cell measurements include red blood cell count (RBC), the hemoglobin concentration, hematocrit, the mean corpuscular volume (MCV), the mean cell hemoglobin (MCH), the mean corpuscular hemoglobin concentration (MCHC), and the red cell distribution width (RDW). The reticulocytes count may also be included.
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The measurement of red blood cells, white blood cells, and platelets is an automated process performed on an instrument. The CBC is performed by flowing the cellular components through a column toward tubes with apertures through which the cells pass and are counted. Cellular components passing through the smallest aperture are counted as platelets. Red blood cells and white blood cells pass through the large apertures and are analyzed by flow cytometry utilizing forward and side light scattered in the circuit to determine the size of red blood cells and identify white blood cell types by size and granularity. This data allows for the identification of five populations: neutrophils, lymphocytes, monocytes, eosinophils, and basophils. Alternatively, red blood cells may be lysed prior to counting of the white blood cells and the hemoglobin measurement is determined from the lysed red blood cells.
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The red blood cell measurements determine the presence of anemia and may provide information on the cause of the anemia. White blood cell measurements include the total number of white blood cells present given by the white blood cell count (WBC) and also a differential including neutrophils, lymphocytes, monocytes, eosinophils, basophils. The ...