Test Quick Guide

Blood is made up of red blood cells (RBC), white blood cells (WBC), and platelets which are suspended in a liquid called plasma. A hematocrit (HCT) lab test determines the percentage of the blood that is composed of RBC.

An HCT test helps your medical provider screen for, diagnose, and monitor conditions that affect your blood or bone marrow. A measurement of HCT is routinely included in a complete blood count (CBC) but may also be ordered on its own if your provider suspects a condition affecting your RBC.

About the Test

Purpose of the test

The purpose of an HCT test is to evaluate the percentage of blood that is made up of RBC. This measurement indicates the viscosity, or thickness, of the blood and depends on the size and number of RBCs in a blood sample. HCT is most often evaluated as part of a CBC, which also includes measurements of RBC, WBC, platelets, and hemoglobin.

Often ordered during a routine medical check-up, a CBC is a common lab test. A CBC that includes HCT may also be ordered to evaluate the cause of certain symptoms, monitor patients receiving medical treatments, and track those with chronic health issues that affect the blood.

What does the test measure?

HCT measures the proportion of the blood that is composed of RBC and is expressed as a percentage.

RBCs are critical for the distribution of oxygen to the body’s cells. Once oxygen is used by cells to produce energy, RBCs transport the waste product, carbon dioxide, from the cells back to the lungs.

HCT levels can be affected by an increase or decrease in the number of RBCs and by changes in other components of the blood. Because HCT measures the percentage of RBC in the blood, relative increases or decreases in other blood components, like plasma or WBC, can lead to abnormal HCT results even if the RBC count is normal.

When should I get this test?

Your provider may test HCT as part of a CBC or if you are experiencing symptoms of an RBC disorder such as anemia. Indications for testing HCT include:

  • Fatigue
  • Moodiness
  • Headaches
  • Brain fog or difficulty concentrating
  • Heavy menstrual flow
  • Poor nutrition
  • Blood in your stools or vomit
  • Cancer and cancer treatment
  • Excessive diarrhea or vomit
  • Leukemia or other conditions associated with bone marrow
  • Chronic health conditions, including kidney diseases

Finding an HCT Test

How can I get an HCT test?

An HCT test requires a sample of blood and is typically ordered by a doctor. A blood draw, also called venipuncture, is conducted by a health provider or a laboratory technician in a medical setting.

Can I take the test at home?

HCT testing is not usually performed at home. Conducting this test requires specialized tools and trained laboratory personnel.

How much does the test cost?

The cost of an HCT test depends on several factors, including other tests performed at the same time and whether or not you have health insurance or are paying out-of-pocket. The cost of HCT testing is often covered by insurance due to the routine nature of the test.

Refer to your health care provider, medical facility, or insurance company for specific details on costs, copays, and deductibles.

Taking an HCT Test

A blood sample is needed for HCT testing. To collect a blood sample, a needle is inserted into your arm and a vial, also known as a vacutainer, is placed on the provider’s end of the needle. The vial is then filled with blood that is used to test your hematocrit.

Before the test

There is no special preparation needed prior to an HCT test, unless specified by your provider.

During the test

Blood draws are a common medical procedure. Usually, blood is drawn from either the top of the hand or the vein on the inside of the elbow. To conduct a blood draw:

  1. An antiseptic wipe is used to cleanse the area prior to the blood draw.
  2. A band is placed around your arm to increase pressure in your vein, making your vein more visible and easier to access.
  3. A needle is placed in your vein and a test tube is attached to the needle and filled with blood.
  4. If you are getting other blood tests in addition to an HCT test you may have more than one vial of blood drawn.

After the test

Once the blood is drawn, the nurse or phlebotomist may ask you to hold pressure on the site of the venipuncture with a cotton swab for a few minutes. They may place a bandage on the cotton swab to maintain pressure.

After any blood draw, you will want to watch out for temporary side effects such as dizziness or lightheadedness. Your provider may want you to stay seated for a few minutes until they can determine that you are safe to get up and walk or drive.

Other than possible lightheadedness and bruising at the site where blood was drawn, there are few potential side effects from a blood draw.

HCT Test Results

Receiving test results

After the test is complete, results will be sent to your doctor for interpretation. HCT test results are most often part of the results of a CBC, which may be available to your doctor within a few minutes or up to several days.

Interpreting test results

HCT test results depend on several factors, including age and sex. The cutoff values for a normal test result, called its reference range, may also vary depending on the laboratory or methods used to conduct the test. Because of the many factors that affect HCT, it’s important to talk to a doctor for support in understanding your test result.

The reference ranges listed below describe common reference ranges for hematocrit:

Hematocrit Reference Ranges for Adults

An abnormal HCT level can indicate that your blood is either too thin or too thick compared to an average person of a similar population.

An abnormally low level of HCT indicates that your cells may not be getting enough oxygen, a condition known as anemia. Abnormally low HCT may be related to a variety of causes, including:

  • Loss of blood
  • Poor nutrition with low intake of iron, vitamin B6, vitamin B12 or folate
  • Bone marrow disorders or cancers such as leukemia, lymphoma, multiple myeloma, or other cancers that spread to the marrow
  • Destruction of RBCs
  • Excessive water in the body

High HCT levels indicate conditions where there is either an overproduction of RBC or an abnormally high concentration of RBCs in your body. Some examples of causes of a high HCT include:

  • Dehydration
  • Lung disease
  • Congenital heart disease
  • Heart failure
  • Certain types of kidney tumors
  • Smoking
  • Living at high altitudes
  • Secondary polycythemia, a rare group of blood disorders caused by heritable changes to genes involved in the production of RBCs causing the body to produce too many RBCs
  • Polycythemia vera, a rare blood disease in which the body produces too many RBCs

Although the results are accurate, laboratory parameters and provider reference ranges as well as personal variables may be subject to differences.

Abnormal HCT test results may or may not require additional follow-up testing. HCT is often evaluated alongside other components of a CBC to look for signs of disease or monitor health conditions.

For example, a doctor may order additional testing if you have low HCT to evaluate the cause of anemia. Testing for anemia may include a reticulocyte count, a renal panel, a liver panel, hemolysis testing, or a blood smear.

Follow-up testing is based on your symptoms, medical history, and the results of other tests. For questions about follow-up testing, speak with your doctor.

Talking with your doctor can help you understand your HCT result and any next steps. You may wish to ask the following questions:

  • What does my result mean for my health?
  • Is there anything I can do to change my HCT levels?
  • Is there any further testing that needs to be done based on my HCT levels?


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