Anemia (American English) or anaemia (Commonwealth English), which literally means "without blood," is a deficiency of red blood cells and/or hemoglobin. This results in a reduced ability of blood to transfer oxygen to the tissues, and this causes hypoxia; since all human cells depend on oxygen for survival, varying degrees of anemia can have a wide range of clinical consequences. Hemoglobin (the oxygen-carrying protein in the red blood cells) has to be present to ensure adequate oxygenation of all body tissues and organs. more...
The three main classes of anemia include excessive blood loss (acutely such as a hemorrhage or chronically through low-volume loss), excessive red blood cell destruction (hemolysis) or deficient red blood cell production. In menstruating women, dietary iron deficiency is a common cause of deficient red blood cell production.
Anemia is the most common disorder of the blood. There are several kinds of anemia, produced by a variety of underlying causes. Anemia can be classified in a variety of ways, based on the morphology of RBCs, underlying etiologic mechanisms, discernible clinical spectra, to mention a few.
Different clinicians approach anemia in different ways; two major approaches of classifying anemias include the "kinetic" approach which involves evaluating production, destruction and loss, and the "morphologic" approach which groups anemia by red blood cell size. (Schier) The morphologic approach uses as its starting point a quickly available and cheap lab test as its starting point (the MCV--see below). On the other hand, focusing early on the question of production (e.g., via the reticulocyte count) may allow the clinician to more rapidly expose cases where multiple causes of anemia may coexist. Regardless of one's philosophy about the classification of anemia, however, methodical clinical evaluation should yield equally good results.
Signs and symptoms
Anemia goes undetected in many people, and symptoms can be vague. Most commonly, people with anemia report a feeling of weakness or fatigue. People with more severe anemia sometimes report shortness of breath. Very severe anemia prompts the body to compensate by markedly increasing cardiac output, leading to palpitations and sweatiness; this process can lead to heart failure in elderly people.
Pallor (pale skin and mucosal linings) is only notable in cases of severe anemia, and is therefore not a reliable sign.
The only way to definitively diagnose most cases of anemia is with a blood test. Generally, clinicians order a full blood count. Apart from reporting the number of red blood cells and the hemoglobin level, the automatic counters also measure the size of the red blood cells by flow cytometry, which is an important tool in distinguishing between the causes of anemia. A visual examination of a blood smear can also be helpful in some cases, and is sometimes a necessity in regions of the world where automated analysis is less accessible.
In modern counters, 4 parameters (RBC Count, hemoglobin concentration, MCV and RDW) are measured, allowing others (hematocrit, mean corpuscular hemoglobin and mean corpuscular hemoglobin concentration) to be calculated, and compared to values adjusted for age and sex. For males, the hemoglobin level that is suggestive of anemia is usually less than 13.0 g/dl, and for females, it is 12.0 g/dl.
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