Hematocrit

HCT, packed cell volume, PCV

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 blood. 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.

You may need this test if it is part of routine blood testing. You may also need your HCT checked before having surgery or if your healthcare provider suspects you have a red blood cell disorder. Too many red blood cells is called polycythemia. Too few red blood cells is called anemia.

Polycythemia may cause:

• Heart attack

• Stroke

• Headache

• Blurred vision

• Itching

• 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

• Fatigue

• Dizziness

• Headache

• Cold, pale skin

• Chest pain

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

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

Test results may vary depending on your age, gender, health history, and other things. Your test results may be different depending on the lab used. They may not mean you have a problem. Ask your healthcare provider what your test results mean for you.

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

• 37% to 47% for women

• 42% to 50% for men

• 31% to 44% for children, depending on 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 or blood volume 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

The test is done with a blood sample. A needle is used to draw blood from a vein in your arm or hand. 

Having a blood test with a needle carries some risks. These include bleeding, infection, bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may feel a slight sting or pain. Afterward, the site may be sore. 

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

Certain medicines can also affect your results.

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