Hematocrit Level Test

Human blood contains 3 components: red blood cells, white blood cells, and platelets. A hematocrit (HCT) test measures the volume of the red blood cells in a specified amount of blood. Hematocrit is calculated in a lab from a blood sample taken from a patient and is expressed as a percentage. This test is usually ordered as part of a complete blood count (CBC) test.

A physician may order the CBC, which includes the hematocrit if a patient is suspected of having anemia, leukemia, or certain nutritional deficiencies.

What Is the Normal Range of Hematocrit?

Hematocrit is calculated in a lab from a sample of blood. Both the number and the size of the red blood cells in the sample will affect the volume of the red blood cells. Different labs will have their own definition of a normal range for a hematocrit level, therefore the normal ranges given in the table below are only one possible example. This test is not specific enough to diagnose any particular disease or disorder, but instead is a tool that can be used in the diagnostic process. If you have questions about your hematocrit level and what it means to your health, consult with your physician.

Why Is a Hematocrit Test Done?

Many factors can affect hematocrit level, including bleeding and bone marrow conditions. Dehydration may suggest a falsely high hematocrit level, which will need to be taken into consideration for those patients that are affected.

A patient who has a low hematocrit level has anemia.

Conditions that may be associated with a low hematocrit level are:

• Bleeding
• Lack of folate, iron, or vitamin B12
• Leukemia
• Side effect of chemotherapy drugs

Conditions that may be associated with a high hematocrit level:

• Dehydration
• Heart disease
• Lung disease (such as hypoxia)
• Polycythemia vera