Red blood cells are made in the bone marrow and carry oxygen from the lungs to the rest of the body using an iron-containing protein called hemoglobin. Red blood cell production requires a natural hormone called erythropoietin, which is produced in the kidneys and stimulates the bone marrow to produce an adequate number of red blood cells. Normal red blood cell production is also dependent on many other factors, including adequate sources of iron, vitamin B-12, folic acid, and trace minerals. The number of red blood cells can be counted directly or can be estimated by the hematocrit or the hemoglobin. The hematocrit (HCT) is the volume percentage of red blood cells in whole blood. Normal HCT values vary, but generally range from 40 to 52 percent in men and 35 to 46 percent in women. Hemoglobin concentration (Hb) is reported as grams of hemoglobin per deciliter of blood (g/dL). Since red blood cells are approximately 33 percent hemoglobin, the hemoglobin result normally is about one third of the HCT. Normal hemoglobin (Hb) values are 14 – 18 g/dl for men and 12 – 16 g/dl for women.Certain diseases and medications can cause the number and percentage of red blood cells to fall below normal levels. When a person becomes anemic, the body tries to compensate in a number of ways. The heart rate increases in an attempt to get more blood, and more oxygen, to the tissues, putting an increased burden on the heart muscle. The respiratory rate also increases. Certain capillary beds (tiny blood vessels in the tissues) open up wider in an attempt to provide more oxygen to vital tissues, while other capillary beds constrict (get smaller) in an attempt to preserve oxygen. This redistribution of blood leads to the common paleness and cold sensation of people with anemia, but provides more oxygen to critical organs such as the heart, brain, and muscles. Increased activity, however, produces and even greater need for oxygen in these tissues, resulting in a sensation of fatigue, weakness, palpitations, shortness of breath, and other symptoms. Anemia, or an abnormally low number of red blood cells, is one of the most common causes of fatigue in people with HIV. As many as 70 to 80 percent of HIV infected patients develop anemia at some time during the course of infection. Moreover, a recent report has concluded that anemia, should it not resolve, is associated with shorter survival of HIV-infected patients.
Posted on: Wed, 28 Aug 2013 07:35:55 +0000
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