Hematocrit Level Test

What to Expect When Undergoing This Test

A hematocrit (HCT) test, also known as the packed-cell volume (PCT), measures how much of your blood consists of red blood cells. Red blood cells carry oxygen from your lungs throughout your body. If you have too many or too few red blood cells, it may be a sign of dehydration, anemia, a vitamin or mineral deficiency, recent or long-term blood loss, or a disease like leukemia, lymphoma, or polycythemia vera, among other things.

This article explores the purpose of the HCT test, how this simple blood test is done, and how results are interpreted by your healthcare provider.

An illustration with information about what to know about the HCT Blood Level Test (hematocrit) test

Illustration by Michela Buttignol for Verywell Health

Purpose of Test 

Red blood cells, also called erythrocytes, are important for distributing oxygen from the lungs to the rest of the body. The percentage of your blood that consists of red blood cells also indicates the (viscosity) thickness of blood.

A high or low result on an HCT test can:

  • Be an early indicator of certain conditions
  • Help diagnose certain diseases
  • Reflect response to certain treatments

An HCT test is usually ordered as part of a complete blood count (CBC) in which multiple tests are run from blood taken at one time. In addition to red blood cells, a CBC evaluates white blood cells (part of the immune system) and platelets (important to stopping bleeding and healing wounds).

Red blood cells contain an important protein called hemoglobin that carries oxygen so it can be delivered throughout your body. Often, a hemoglobin (Hgb) test is done with an HCT blood test and as part of a CBC. The pair of tests are commonly referred to as an H and H test.

Commonly, healthcare providers use the HCT, as well as hemoglobin, to check for anemia, a blood disorder that's characterized by a low red blood cell (RBC) count.

The most common cause of anemia is iron deficiency. Anemia can also be a side effect of cancer treatments, such as chemotherapy and radiation. Hematocrit results enable healthcare providers to manage anemia if it develops.

Symptoms of anemia include:

  • Fatigue
  • Headaches
  • Dizziness
  • Feeling cold
  • Shortness of breath

Procedure

As a basic blood test, the HCT doesn’t require fasting or special considerations. Blood is drawn from the inside of the elbow or the back of the hand. With infants and young children, it may involve a small puncture in the heel or fingertip to collect blood onto a test strip.

If a hematocrit test is taken as part of a complete blood count, you may need to have more than one vial of blood drawn.

In addition to the full CBC, other tests may be performed at the same time or as a follow-up to help with a diagnosis, including:

  • A blood smear: A small blood sample is examined under a microscope for signs of problems
  • Reticulocyte count: A blood test that determines how well your bone marrow (the spongy tissue inside bones) makes RBCs
  • Iron studies: A group of blood tests interpreted together to check for iron deficiency or iron overload
  • Vitamin B12 and folate levels: A test to see if you have enough of the nutrients needed to create blood cells

How Blood Is Tested

Once your blood is collected, it’s placed in a centrifuge or an automated hematology analyzer instrument.

The centrifuge separates the red blood cells from the plasma (non-cellular liquid), white blood cells, and platelets, giving a direct measure of the percentage of RBCs in the blood sample.

Automated instruments determine the hematocrit (a calculated value) through several methods. Some instruments measure/count cells through electrical impedance (Coulter principle), some measure/count cells with a laser beam, and some measure/count cells by adding fluorescent reagents. Whichever method is used, the hematocrit is calculated from the RBC cell count (RBC), mean cell volume (MCV), and the total sample volume (RBC x MCV/10 = Hct).

Interpreting Results

Age and gender affect hematocrit level, but general guidelines for normal levels in adults and young children are as follows:

 Age  Normal Levels
 0 to 3 days  45% to 67%
 3 days to 1 week  42% to 66%
 1 to 2 weeks  39% to 63%
 2 weeks to 1 month  31% to 55%
 1 to 2 months  28% to 42%
 2 to 6 months  29% to 41%
 6 months to 2 years  33% to 39%
 2 to 6 years  34% to 40%
 6 to 12 years  35% to 45%
 12 years to adult (females)  36% to 46%
 12 to 18 years (males)  37% to 49%
 18 years to adult (males)  41% to 53%

If your levels are above or below normal, one of these serious health issues could be the reason why:

Below Normal (Anemia) Above Normal
Iron or vitamin deficiency including folate, B12, or B6   Dehydration
Too much water in the body Smoking
Thyroid problems Elevated testosterone levels 
Autoimmune disease, such as Evans syndrome  Obstructive sleep apnea
Blood loss due to internal or external trauma Heart disease 
Kidney disease Carbon monoxide poisoning
Leukemia, lymphoma, or other bone marrow cancers   Scarring/thickening of the lungs
Bone marrow damage from chemotherapy or toxins PV/other blood-related disease 

HCT test results may be affected by factors such as:

  • Recent blood transfusion
  • Pregnancy
  • Living at a high altitude

Your healthcare provider will take these factors into account when interpreting the results.

Follow-Up

Your healthcare provider will review with you the results of the HCT and all other tests that were done. Depending on the practice, this may be done in person, over the phone, or via a secured message.

If your hematocrit results are outside the normal range, your healthcare provider may have you come in for additional blood tests to help diagnose the cause.

If test results point to a bone marrow problem, a bone marrow examination may be needed. A sample of bone marrow is taken, usually from the hip, to check for lymphoma and similar disorders.

Your healthcare provider may want to repeat the HCT test after weeks, months, or at least annually to monitor your levels.

Balancing Levels

If your results, along with other tests, indicate that you have iron-deficiency anemia, you can usually improve your red blood cell count by fortifying your diet with iron-rich foods.

Some examples of iron-rich foods include:

  • Red meat
  • Chicken
  • Liver
  • Eggs
  • Shrimp
  • Tuna
  • Spinach
  • Peas
  • Broccoli
  • Whole wheat bread
  • Tofu
  • Beans

Your healthcare provider may also suggest using over-the-counter iron supplements. If the iron deficiency anemia is severe, a blood transfusion may be needed.

If anemia is the result of a bacterial infection, you may need to begin antibiotics.

If you have a condition that causes overproduction of RBCs, your healthcare provider may suggest lifestyle changes such as quitting smoking or adopting a heart-healthy diet. In the rare case of PV, a healthcare provider can provide medication that will help you manage the condition, but it cannot be cured.

Summary

A hematocrit test gives your healthcare provider important information about your health. The test measures red blood cells, which have a protein that delivers oxygen throughout your body. The hematocrit level can help to diagnose or monitor blood disorders, dehydration, nutrient deficiencies, blood-related cancers, and many other conditions.

If your test results are abnormal, other tests may be performed at the same time or afterward to help identify the cause of anemia (low hematocrit) or high red blood cell counts, so you can get the right treatment.

Frequently Asked Questions

  • How can I lower my hematocrit levels?

    Sometimes dehydration can cause high hematocrit levels. In this case, drinking lots of fluids can bring your levels back to normal. Making lifestyle changes such as quitting smoking and eating a heart-healthy diet may also help lower levels.

  • What does it mean if hematocrit is low?

    A low hematocrit number means that your body doesn't have enough red blood cells in your blood. This is also called anemia.

  • What hematocrit level is considered anemic?

    For men, a hematocrit level of less than 41% is considered anemic. For women, that number is slightly lower at less than 36%. The number varies for children depending on their age.

  • What does it mean if my hemoglobin is high?

    Hemoglobin is a protein in the red blood cells that carries oxygen throughout your body. High hemoglobin levels are usually caused by an extended period of low oxygen in the blood. This may be due to a number of causes, from dehydration to heart or lung disorders.

10 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. U.S. National Library of Medicine. MedlinePlus. Hematocrit test.

  2. National Cancer Institute. Anemia: Cancer Treatment Side Effect.

  3. U.S. National Library of Medicine. MedlinePlus. Anemia.

  4. Avecilla S, Marionneaux S, Leiva T, et al. Comparison of manual hematocrit determinations versus automated methods for hematopoietic progenitor cell apheresis products. Transfusion. 2016;56(2):528-32. doi: 10.1111%2Ftrf.13346

  5. Seattle Children's Lab. Hematocrit.

  6. American Red Cross. Iron Rich Foods.

  7. National Heart, Lung, and Blood Institute. Iron-deficiency anemia.

  8. National Heart, Lung, and Blood Institute. Polycythemia Vera.

  9. American Red Cross. What does hematocrit mean?

  10. Mount Sinai. Hemoglobin.

By Amber J. Tresca
Amber J. Tresca is a freelance writer and speaker who covers digestive conditions, including IBD. She was diagnosed with ulcerative colitis at age 16.