Does this test have other names?

HCT, packed cell volume, PCV

What is this test?

This test measures how much of your blood is made up of red blood cells.

Normal blood contains white blood cells, red blood cells, platelets, and the fluid portion called plasma. The word hematocrit means to separate. In this test, your red blood cells are separated from the rest of your blood so they can be measured.

Your hematocrit (HCT) shows whether you have a normal amount of red blood cells, too many, or too few. To measure your HCT, your blood sample is spun at a high speed to separate the red blood cells.

Why do I need this test?

You may need this blood test as part of routine blood testing. You may also need your hematocrit checked before having surgery or if your doctor suspects you have a red blood cell disorder. Too many red blood cells, or thick blood, is called polycythemia. Too few red blood cells, or thin blood, is called anemia.

Polycythemia may cause:

  • Heart attack

  • Stroke

  • Headache

  • Blurred vision

  • Dizziness

Anemia can be caused by blood loss, your body making fewer red blood cells, or increased destruction of red blood cells. Symptoms may include:

  • Shortness of breath

  • Dizziness

  • Headache

  • Cold, pale skin

  • Chest pain

What other tests might I have along with this test?

Your doctor may also order a complete blood count, or CBC, which is a blood test that counts all the different types of cells in your blood.

Your doctor may also order a test that measures your hemoglobin to find out how much oxygen your red blood cells are carrying.

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

Results are given as a percentage. Normal hematocrit values are different for men, women, and children. Normal values are:

  • 36 to 48 percent for women

  • 42 to 52 percent for men

  • 30 to 44 percent for children, depending upon age

If your HCT is high, it may mean your body is making too many red blood cells. Your HCT may also be high if your plasma is too low. This can happen when you are dehydrated or in shock.

If your HCT is low, it means you may have:

  • Anemia

  • White blood cell cancers, such as leukemia

  • Chronic illness

  • Bleeding

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

What might affect my test results?

Living at a high altitude may cause your HCT to be higher than normal. Being pregnant or being older than 60 can cause your HCT to be lower than normal.

Certain drugs can also affect your results.

How do I get ready for this test?

You don't need to prepare for this test. But be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.