Hematocrit

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 red blood cells.

An HCT test helps your medical provider screen for, diagnose, and monitor conditions that affect your blood or bone marrow. A measurement of hematocrit 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 red blood cells.

Purpose of the test

The purpose of a hematocrit test is to evaluate the percentage of the blood that is made up of red blood cells. This measurement indicates the viscosity, or thickness, of the blood and depends on the size and number of RBCs in a blood sample. Hematocrit is most often evaluated as part of a complete blood count, which also includes measurements of red blood cells, white blood cells, platelets, and hemoglobin.

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

What does the test measure?

Hematocrit measures the proportion of the blood that is composed of red blood cells and is expressed as a percentage.

Red blood cells 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.

Hematocrit levels can be affected by an increase or decrease in the number of red blood cells and by changes in other components of the blood. Because hematocrit measures the percentage of red blood cells in the blood, relative increases or decreases in other blood components, like plasma or white blood cells, can lead to abnormal hematocrit results even if the red blood cell count is normal.

When should I get a hematocrit test?

Your provider may test hematocrit as part of a CBC or if you are experiencing symptoms of a RBC disorder such as anemia. Indications for testing hematocrit 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 disease

How to get tested

A hematocrit 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?

Hematocrit 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 a hematocrit test depends on several factors, including other tests performed at the same time and whether or not the patient has health insurance or is paying out-of-pocket. The cost of hematocrit 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.

A blood sample is needed for hematocrit 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 a hematocrit test, unless specified by your provider.

During the test

Blood draws are a common medical procedure. Blood is most often 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 a hematocrit 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.

Receiving test results

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

Interpreting test results

Although a hematocrit level is measured as a percentage, lab reports may or may not include a percentage symbol. For example, a test result may simply say 45 rather than 45%.

Normal hematocrit test results depend on several factors, including age, sex, pregnancy status, and the altitude at which the patient lives. 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 hematocrit, 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:

An abnormal hematocrit 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 hematocrit indicates that your cells may not be getting enough oxygen, a condition known as anemia. Abnormally low hematocrit 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 hematocrit levels indicate conditions where there is either an overproduction of red blood cells or an abnormally high concentration of RBCs in your body. Some examples of causes of a high hematocrit 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

Are test results accurate?

Yes. Hematocrit tests are accurate. No test result is perfect, but if there is any suspicion the test results are not accurate your provider will order another test to confirm the results. Although the results are accurate, laboratory parameters and provider reference ranges as well as personal variables may be subject to differences.

Do I need follow-up tests?

Abnormal hematocrit test results may or may not require additional follow-up testing. Hematocrit 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 for a patient with low hematocrit in order 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 each patient’s symptoms, medical history, and the results of other tests. For questions about follow-up testing, patient’s should speak with their doctor.

Questions for your doctor about test results

Talking with your doctor can help you understand your hematocrit 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 hematocrit levels?
• Is there any further testing that needs to be done based on my hematocrit levels?

How is a hematocrit test different from other components of a complete blood count?

A complete blood count measures several components of the blood, including red blood cells, white blood cells, platelets, hematocrit and hemoglobin. Hematocrit is the percentage of your blood made up of red blood cells, calculated using the volume and size of RBCs. Simply stated hematocrit defines the viscosity of your blood, whether thick or thin.

Whereas hematocrit is the overall percentage of red blood cells in your total blood volume, hemoglobin is the iron-containing protein found in all red blood cells (RBCs) that gives the cells their characteristic red color. Hemoglobin enables RBCs to bind to oxygen in the lungs and carry it to tissues and organs throughout the body.

White blood cells are not related to hematocrit directly. White blood cells, also called leukocytes, are an important part of the body’s defense system. They help protect against infections and also have a role in inflammation and allergic reactions.

Platelets, also called thrombocytes, are tiny fragments of cells that are essential for normal blood clotting. The platelet count is a test that determines the number of platelets in your sample of blood.

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