Increased viscosity also contributes to high blood pressure, sluggish blood flow and increased risk of stroke. This raises the viscosity of blood, the blood can becomes thickened which increases the resistance to flow and makes the blood more difficult for the heart to pump. In polycythemia (too many red blood cells) the percentage of red blood cells (RBCs) is abnormally high, and the hematocrit may be 65% or higher. In anemia, the body does not have the capacity to deliver enough oxygen to tissues and organs, causing fatigue and weakness. A significant drop in hematocrit indicates anemia, a lower-than-normal number of red blood cells (RBCs). If the bone marrow is not able to produce new red blood cells fast enough, then the overall number of red blood cells and hematocrit will drop, resulting in anemia. In general, the hematocrit will rise when the number of red blood cells increases and the hematocrit will fall to less than normal when there is a drop in production of red blood cells by the bone marrow, an increase in the destruction of red blood cells, or if blood is lost due to bleeding. If the size of the red blood cells decreases (MCV decreases), so will the hematocrit and vice versa. The hematocrit reflects both the number of red blood cells and their volume (mean corpuscular volume or MCV). A sample is obtained by drawing blood through a needle placed in a vein in the arm or by a fingerstick (for children and adults) or a heelstick (for newborns). It is often performed in conjunction with a hemoglobin (Hb) level and is also one component of the complete blood count (CBC), a test that is often used in the general evaluation of a person’s health. The hematocrit is a fairly quick and simple way of evaluating a person’s red blood cells and checking for conditions such as anemia.
Lower hematocrit values in women during their reproductive years also may be due to excessive loss of blood during menstruation. Thus, testosterone contributes to higher hematocrits in males. The hormone testosterone, present in much higher concentration in males than in females, stimulates synthesis of erythropoietin (EPO), the hormone that in turn stimulates production of red blood cells (RBCs). A hematocrit of 40 indicates that 40% of the volume of blood is composed of red blood cells (RBCs). The normal hematocrit range for adult males is 40 to 54% (average = 47%) for adult females it is 38 to 46% (average = 42%). Platelets stick together to seal small cuts or breaks on blood vessel walls and stop bleeding. White blood cells (WBCs) and platelets (thrombocytes) also are made in your bone marrow. Red blood cells are made in your bone marrow-a sponge-like tissue inside the bones. They also remove carbon dioxide (a waste product) from your body’s cells and carry it to the lungs to be exhaled. Red blood cells carry oxygen to all parts of your body. For example, a hematocrit value of 40% means that there are 40 milliliters of red blood cells in 100 milliliters of blood. The value is expressed as a percentage or fraction. The hematocrit is a ratio of the volume of red blood cells to the volume of all these components together, called whole blood. Blood consists of red blood cells (RBCs), white blood cells (WBCs), and platelets (thrombocytes) suspended in a fluid portion called plasma (see Figure 1). The hematocrit measures the volume of red blood cells (RBCs) compared to the total blood volume (red blood cells, white blood cells, platelets and plasma). Hematocrit is a blood test that measures the proportion of a person’s blood that is made up of red blood cells (RBCs) or the percentage of total blood volume occupied by red blood cells (RBCs).
Who Is at Risk for Iron-Deficiency Anemia ?.What Are the Signs and Symptoms of Anemia ?.High Rates of Red Blood Cell Destruction.There are many types of anemia with specific causes and traits.What happens when you have low red blood cells (Anemia).Dietary Factors Affecting Red Blood Cell Production.
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