Hematocrit

Also known as: Hct; Crit; Packed cell volume (PCV)

Formal name: Hematocrit

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 (mean corpuscular volume or 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).

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.