Hematocrit Test

A hematocrit test is a blood test that measures the amount (percent) of your blood that is made up of red blood cells. Red blood cells carry oxygen from your lungs to the rest of your body. The other parts of your blood include white blood cells (to help fight infection and other diseases), platelets (to help make blood clots to stop bleeding), and a liquid called plasma.

Hematocrit levels that are too high or too low can be a sign of a blood disorder, dehydration, or other medical conditions that affect your blood.

Why this test is done

Your health care provider may order a hematocrit test as part of your routine checkup or to monitor your health if you are being treated for cancer or have an ongoing health condition. Your provider may also order this test if you have symptoms of a red blood cell disorder, such as anemia or polycythemia:

Symptoms of anemia (too few red blood cells) may include:

• Shortness of breath
• Weakness or fatigue
• Headache
• Dizziness
• Arrhythmia (a problem with the rate or rhythm of your heartbeat)

Symptoms of polycythemia (too many red blood cells) may include:

• Headache
• Feeling light-headed or dizzy
• Shortness of breath when lying down
• Weakness or fatigue
• Skin symptoms such as itching after a shower or bath, burning, or a red face
• Heavy sweating, especially during sleep
• Blurred or double vision and blind spots
• Unusual bleeding, such as bleeding gums or nosebleeds

How to prepare

You don't need any special preparations for a hematocrit test. If your provider has ordered more tests on your blood sample, you may need to fast (not eat or drink) for several hours before the test. Your provider will let you know if there are any special instructions to follow.

Sample type

Blood

Other names for this test

HCT, packed cell volume, PCV, Crit; H and H (Hemoglobin and Hematocrit)