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Hematocrit Blood Test

What is a hematocrit blood test?

The hematocrit blood test determines the percentage of red blood cells (RBC's) in the blood. Blood is composed mainly of red blood cells and white blood cells suspended in an almost clear fluid called serum. The hematocrit test indicates the percentage of blood by volume that is composed of red blood cells. The condition called "anemia" results from having too few red blood cells. Anemia causes a variety of symptoms. The hematocrit is a basic test that can tell a physician a lot about a person's health. 

Picture of Red Blood Cells

How is the hematocrit measured?

In most labs, the hematocrit is measured by a machine that automatically determines a variety of blood tests referred to as the blood count (CBC). The complete blood count is a numerical listing of the hematocrit, as well as the hemoglobin concentration, and the three blood cell lines produced by the bone marrow (the red blood cells, the white blood cells, and the platelets).

Another simple method is termed the spun hematocrit or "spun crit." A small amount of blood (about 0.05 to 0.1ml) is placed in a thin capillary tube, the tube is sealed with wax or clay, and then placed in a centrifuge to be spun. The red cells collect at the bottom and form a red column and are separated from the straw-colored serum column by a small area composed of white blood cells. The height of the total blood in the capillary tube (red cells, white cells and serum equals 100%). The height of the red cell column divided by the height of the total fluid in the capillary tube equals the hematocrit (percentage of RBC's in the total blood volume). This test can be performed in a few minutes.

Medically Reviewed by a Doctor on 9/19/2016

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Hematocrit - Low Reading

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Hematocrit - Results

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