Hematocrit test

Hematocrit (he-MAT-uh-krit) is the proportion of your total blood volume that is composed of red blood cells. A hematocrit (Hct) test indicates whether you have too few or too many red blood cells — conditions that can occur as the result of certain diseases. Red blood cells, or erythrocytes (uh-RITH-roe-sites), transport oxygen throughout your body.

A hematocrit test is done using a sample of your blood. A lab technician puts the sample in a device called a centrifuge that spins the blood very quickly in a test tube. This motion separates your blood into three parts: the fluid component (plasma), red blood cells and other blood cells. When the blood is separated, the technician can determine what proportion of the cells are red blood cells. Hematocrit is also called packed-cell volume (PCV).


Why it's done How you prepare What you can expect Results

A hematocrit test is part of a complete blood count (CBC). The proportion of red blood cells compared with all blood cells may help your doctor make a diagnosis or monitor your response to a treatment.

A lower than normal hematocrit may indicate:

  • An insufficient supply of healthy red blood cells (anemia)
  • A large number of white blood cells — usually a very small portion of your blood — due to long-term illness, infection, leukemia, lymphoma or other disorders of white blood cells
  • Vitamin or mineral deficiencies
  • Recent or long-term blood loss

A higher than normal hematocrit may indicate:

  • Dehydration
  • A disorder, such as polycythemia vera, that causes your body to produce too many red blood cells
  • Lung or heart disease — if the body senses low oxygen levels, it will make more red blood cells in an effort to increase the amount of oxygen in the blood
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