Hematocrit Test

At a Glance

Also known as

Hct, Crit, Packed cell volume (PCV)

Related tests

Complete blood count

Why get tested?

If your doctor suspects that you have anemia, polycythemia, or dehydration

When to get tested?

As part of a complete blood count (CBC), which may be ordered for a variety of reasons

Sample required

A blood sample drawn from a vein in your arm or by a fingerstick (children and adults) or heelstick (newborns)

The Test Sample

What is being tested?

Hematocrit is a measurement of the proportion of blood that is made up of red blood cells. The value is expressed as a percentage or fraction of cells in blood. For example, a hematocrit value of 40% means that there are 40 milliliters of red blood cells in 100 milliliters of blood.

The hematocrit rises when the number of red blood cells increases or when the plasma volume is reduced, as in dehydration. The hematocrit falls to less than normal, indicating anemia, when your body decreases its production of red blood cells or increases its destruction of red blood cells or if blood is lost due to bleeding.

The hematocrit reflects both the number of red cells and their volume (MCV). If the size of the red cell decreases, so will the hematocrit and vice versa.

How is the sample collected for testing?

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).

The Test

How is it used?

This test is used to evaluate:

  • anemia (decrease of red blood cells), 

  • polycythemia, 

  • response to treatment of anemia or polycythemias, 

  • dehydration, 

  • blood transfusion decisions for severe symptomatic anemias, and

  • the effectiveness of those transfusions.

When is it ordered?

The hematocrit is normally ordered as a part of the complete blood count (CBC). It is also repeated at regular intervals for many conditions, including:

  • the diagnosis of anemia and polycythemia, 

  • the monitoring of treatment for anemia, 

  • recovery from dehydration, and

  • monitoring of ongoing bleeding to check its severity.

What does the test result mean?

Decreased hematocrit indicates anemia, such as that caused by iron deficiency or other deficiencies. Further testing may be necessary to determine the exact cause of the anemia.

Other conditions that can result in a low hematocrit include vitamin or mineral deficiencies, recent bleeding, cirrhosis of the liver, and malignancies.

The most common cause of increased hematocrit is dehydration, and with adequate fluid intake, the hematocrit returns to normal. However, it may reflect a condition called polycythemia veraÂ?that is, when a person has more than the normal number of red blood cells. This can be due to a problem with the bone marrow or, more commonly, as compensation for inadequate lung function (the bone marrow manufactures more red blood cells in order to carry enough oxygen throughout your body). Anytime a hematocrit is persistently high, the cause should be determined in consultation with a doctor.

With regard to transfusions, this is normally not considered for otherwise healthy persons as long as the hemoglobin level is above 8 grams per deciliter or the hematocrit is above 24%.

Is there anything else I should know?

Pregnancy usually causes slightly decreased hematocrit values due to extra fluid in the blood.

Living at high altitudes causes increased hematocrit values - this is your body’s response to the decreased oxygen available at these heights.

Common Questions

  1. How do you treat anemia?

    Treatment will depend upon the type of anemia and the cause. Folic acid, vitamin replacement, iron, and red blood cell (RBC) transfusion are some therapies used to treat anemia.

  2. Can I test for hematocrit at home?

    No. This test is performed by trained laboratory personnel.

  3. Is anyone more at risk for abnormal hematocrit values? 

    People who have a chronic illness (such as rheumatoid arthritis), an inherited blood disorder, or malnutrition are at risk for abnormally low hematocrits. Women of childbearing age may have temporary decreases in hematocrit during menstrual periods and pregnancy. Women of childbearing age are more at risk of developing low hematocrits due to iron deficiency.

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