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INTRODUCTION

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LEARNING OBJECTIVES

After studying this chapter, you should:

  • Understand how anemia impacts oxygen transport and the ways in which anemic patients compensate for decreased oxygen-carrying capacity.

  • Develop a coherent approach to the clinical and laboratory evaluation of patients with anemia.

  • Understand and use classification of anemia based on production versus destruction and on red cell size (mean cell volume).

  • Be able to explain the phenomenon of ineffective erythropoiesis, including its diagnosis and role in pathogenesis.

  • Understand the process by which red cells are broken down, the catabolism of heme in macrophages, and the transport of bilirubin in the plasma and its conjugation in the liver.

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Anemia is a serious and highly prevalent worldwide health problem. As shown in Figure 3-1A, the disabling impact of anemia is considerably higher in developing nations, particularly tropical areas where infections and inherited hemoglobin disorders are endemic. Iron deficiency is the most common cause of anemia in all parts of the world (Figure 3-1B), but malaria, hookworm, schistosomiasis, tuberculosis, and human immunodeficiency virus (HIV) also are frequently encountered in tropical areas. As explained in Chapters 8 and 9, sickle cell disease and thalassemia are prevalent in these regions because they confer protection against malaria caused by Plasmodium falciparum. Individuals afflicted by more than one of these disorders are not uncommon, and such combinations can be devastating. For example, the hemoglobin level in a patient with sickle cell disease can fall to an alarming degree in the presence of malaria or HIV infection. Other, primarily infectious, causes of anemia that are prevalent in tropical regions of the developing world are beyond the scope of this book.

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FIGURE 3-1

A) Worldwide distribution and health impact of anemias in 2010. Colors indicate years of life with disability per 10,000 people, and serve to highlight the markedly adverse impact of anemias in sub-Saharan Africa. B) Prevalence of anemia by etiology in 2010. CKD, chronic kidney disease; G6PD, glucose-6-phosphate dehydrogenase; NTD, neglected tropical diseases. (Reproduced with permission from Kassebaum NJ, Jasrasaria R, Naghavi M, et al. A systematic analysis of global anemia burden from 1990 to 2010. Blood 2014;123(5):615–624.)

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DEFINITION OF ANEMIA

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As stated in Chapter 1, the primary function of the red blood cell is to transport oxygen to respiring cells and tissues. Anemia is defined as a significant deficit in the mass of circulating red blood cells. As a result, the capacity of the blood to deliver oxygen is compromised. The presence of anemia is documented by measuring either the concentration of hemoglobin in the blood or the hematocrit, which is the ratio of the volume of red cells to the total volume of a blood sample. A patient is anemic if the hemoglobin ...

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