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Hematocrit Test
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Lab Tests

Hematocrit Test

A hematocrit test measures the percentage of your blood made up of red blood cells, helping to diagnose conditions like anemia or polycythemia.

What is a 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.

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

What is it used for?

A hematocrit (HCT) test is often part of a complete blood count (CBC). A CBC is a common blood test that measures the number and type of cells in your blood. It is used to check your general health and to monitor or help diagnose blood disorders, such as anemia (not enough red blood cells) or polycythemia (erythrocytosis), an uncommon disorder where you have too many red blood cells and your blood becomes too thick.

Why do I need a hematocrit test?

Your health care provider may order this test as part of a routine checkup, to monitor a health condition, or if you have symptoms of a red blood cell disorder.

Symptoms of anemia (too few red blood cells)

  • 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)

  • 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

What happens during a hematocrit test?

A health care professional will take a blood sample from a vein in your arm using a small needle. A small amount of blood is collected into a test tube or vial. The process usually takes less than five minutes.

Preparation and Risks

There are no special preparations required for a hematocrit test unless your provider has ordered additional tests that require fasting. There is very little risk to the test, though you may experience slight pain or bruising at the needle site.

What do the results mean?

Results are reported as a percentage of your blood made up of red blood cells. Normal levels vary based on sex, age, smoking status, and altitude.

Lower-than-normal hematocrit

  • Recent injury or chronic blood loss
  • Anemia
  • Bone marrow disease
  • Certain cancers, including leukemia, lymphoma, or multiple myeloma

Higher-than-normal hematocrit

  • Lung disease, congenital heart disease, or heart failure
  • Polycythemia
  • Dehydration (the most common cause)
  • Shock

Note: Living at high altitudes or being pregnant can also affect your results. Always discuss your specific results with your health care provider.

Frequently Asked Questions

low hematocrit indicates fewer red blood cells to carry oxygen, which can lead to reduced oxygen delivery to muscles and tissues. This often manifests as persistent fatigue, shortness of breath during mild exertion, and a general sense of weakness, especially when you try to stay active or climb stairs.
Yes, dehydration concentrates the blood and can artificially raise hematocrit. Drink plenty of water for at least 24 hours before the draw, avoid alcohol and diuretics on the day of the test, and inform your provider if you have been ill or had a fever.
Your clinician will tailor the frequency to your condition. For stable anemia, a repeat test every 3–6 months is common, while those with polycythemia or on treatment may need checks every 1–3 months to monitor red‑cell mass and adjust therapy.
Maintain adequate hydration, avoid smoking, limit alcohol, and incorporate regular aerobic exercise. A diet low in iron‑rich foods and high in fiber can help, but always discuss dietary changes with your provider, especially if you’re on medication for polycythemia.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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