Also Known As
Packed Cell Volume
H and H (Hemoglobin and Hematocrit)
Formal Name
This article was last reviewed on
This article waslast modified on
January 15, 2018.
At a Glance
Why Get Tested?

To determine the proportion of your blood that is made up of red blood cells (RBCs) in order to screen for, help diagnose, or monitor conditions that affect RBCs; as part of a routine health examination or if your healthcare provider suspects that you have anemia or polycythemia

When To Get Tested?

With a test for hemoglobin or as part of a complete blood count (CBC) during a routine health exam or when you have signs and symptoms of anemia (weakness, fatigue) or polycythemia (dizziness, headache); at regular intervals to monitor a disorder that affects RBCs and to evaluate the effectiveness of treatment

Sample Required?

A blood sample drawn from a vein in your arm or by a fingerstick (children and adults) or heelstick (newborns)

Test Preparation Needed?


You may be able to find your test results on your laboratory's website or patient portal. However, you are currently at Lab Tests Online. You may have been directed here by your lab's website in order to provide you with background information about the test(s) you had performed. You will need to return to your lab's website or portal, or contact your healthcare practitioner in order to obtain your test results.

Lab Tests Online is an award-winning patient education website offering information on laboratory tests. The content on the site, which has been reviewed by laboratory scientists and other medical professionals, provides general explanations of what results might mean for each test listed on the site, such as what a high or low value might suggest to your healthcare practitioner about your health or medical condition.

The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.

If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.

Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called "normal" values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.

While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are "within normal limits."

For more information, please read the article Reference Ranges and What They Mean.

Hematocrit Reference Range

The reference ranges1 provided here represent a theoretical guideline that should not be used to interpret your test results. Some variation is likely between these numbers and the reference range reported by the lab that ran your test. Please consult your healthcare provider.

Age Conventional Units2 SI Units3
 0-18 years Not available due to wide variability. See child's lab report for reference range.
Adult male 41.5-50.4% 0.415-0.504 volume fraction
Adult female 36.9-44.6% 0.369-0.446 volume fraction

1from Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. McPherson R, Pincus M, eds. Philadelphia, PA: Elsevier Saunders; 2011.

2 Conventional Units are typically used for reporting results in U.S. labs

3 SI Units are used to report lab results outside of the U.S.

What is being tested?

A hematocrit is a test that measures the proportion of a person's blood that is made up of red blood cells (RBCs). Blood consists of RBCs, white blood cells (WBCs), and platelets suspended in a fluid portion called plasma. The hematocrit is a ratio of the volume of red blood cells to the volume of all these components together, called whole blood. The value is expressed as a percentage or fraction. For example, a hematocrit value of 40% means that there are 40 milliliters of red blood cells in 100 milliliters of blood.

The hematocrit is a fairly quick and simple way of evaluating a person's red blood cells and checking for conditions such as anemia. It is often performed in conjunction with a hemoglobin level and is also one component of the complete blood count (CBC), a test that is often used in the general evaluation of a person's health.

RBCs are produced in the bone marrow and are released into the bloodstream when they are, or nearly are, mature. They typically make up roughly 37% to 49% of the volume of blood. RBCs contain hemoglobin, a protein that binds to oxygen. The primary function of RBCs is to carry oxygen from the lungs to the tissues and organs of the body. They also transport a small portion of carbon dioxide, a byproduct of cell metabolism, from tissues and organs back to the lungs, where it is expelled.

The typical lifespan of an RBC is 120 days and the bone marrow must continually produce new RBCs to replace those that age and degrade or are lost through bleeding. A number of conditions can affect either the production of new RBCs by the bone marrow or the lifespan of those in circulation or that result in significant bleeding.

The hematocrit reflects both the number of red blood cells and their volume (mean corpuscular volume or MCV). If the size of the RBCs decreases, so will the hematocrit and vice versa. In general, the hematocrit will rise when the number of red blood cells increases and the hematocrit will fall to less than normal when there is a drop in production of RBCs by the bone marrow, an increase in the destruction of RBCs, or if blood is lost due to bleeding. If the bone marrow is not able to produce new RBCs fast enough, then the overall number of RBCs and hematocrit will drop, resulting in anemia.

In anemia, the body does not have the capacity to deliver enough oxygen to tissues and organs, causing fatigue and weakness. In polycythemia, too many RBCs are produced (resulting in increased hematocrit) and the blood can become thickened, causing sluggish blood flow and related problems.

How is the sample collected for testing?

A sample is obtained by drawing blood through a needle placed in a vein in the arm or by a fingerstick (for children and adults) or a heelstick (for newborns).

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

Accordion Title
Common Questions
  • How is it used?

    The hematocrit test is often used to check for anemia, usually along with a hemoglobin test or as part of a complete blood count (CBC). The test may be used to screen for, diagnose, or monitor a number of conditions and diseases that affect the proportion of the blood made up of red blood cells (RBCs). RBCs circulate in the blood and carry oxygen throughout the body. (For more, see the "What is being tested?" section.)

    A hematocrit may be used to:

    • Identify and evaluate the severity of anemia (low RBCs, low hemoglobin, low hematocrit) or polycythemia (high RBCs, high hemoglobin, high hematocrit)
    • Monitor the response to treatment of anemia or polycythemia and other disorders that affect RBC production or lifespan
    • Help make decisions about blood transfusions or other treatments if anemia is severe
    • Evaluate dehydration

    Some conditions affect RBC production in the bone marrow and may cause an increase or decrease in the number of mature RBCs released into the blood circulation. Other conditions may affect the lifespan of RBCs in the circulation. If there is increased destruction of RBCs (hemolysis) or loss of RBCs (bleeding) and/or the bone marrow is not able to produce new ones fast enough, then the overall number of RBCs and hematocrit will drop, resulting in anemia.

    The hematocrit can indicate if there is a problem with RBCs, but it cannot determine the underlying cause. In addition to the full CBC, some other tests that may be performed at the same time or as follow up to establish a cause include a blood smear, reticulocyte count, iron studies, vitamin B12 and folate levels, and in more severe conditions, a bone marrow examination.

  • When is it ordered?

    The hematocrit is routinely ordered as a part of the complete blood count (CBC). It may also be ordered by itself or with a hemoglobin level as part of a general health examination. These tests are often ordered when a person has signs and symptoms of a condition affecting RBCs, such as anemia and polycythemia.

    Some signs and symptoms of anemia include:

    • Weakness or fatigue
    • Lack of energy
    • Fainting
    • Paleness (pallor)
    • Shortness of breath

    Some signs and symptoms of polycythemia include:

    • Disturbed vision
    • Dizziness
    • Headache
    • Flushing
    • Enlarged spleen

    A hematocrit may sometimes be ordered when someone has signs and symptoms of serious dehydration, such as extreme thirst, dry mouth or mucous membranes, and lack of sweating or urination.

    This test may be performed several times or on a regular basis when someone has been diagnosed with ongoing bleeding problems, anemia, or polycythemia to determine the effectiveness of treatment. It may also be ordered routinely for people undergoing treatment for cancer that is known to affect the bone marrow.

  • What does the test result mean?

    Red blood cells (RBCs) typically make up roughly 37% to 49% of the volume of blood.

    Since a hematocrit is often performed as part of a complete blood count (CBC), results from other components, such as RBC count, hemoglobin, reticulocyte count, and/or red blood cell indices, are taken into consideration. Age, sex, and race are other factors to be considered. In general, the hematocrit mirrors the results of the RBC count and hemoglobin.

    A low hematocrit with low RBC count and low hemoglobin indicates anemia. Some causes include:

    A high hematocrit with a high RBC count and high hemoglobin indicates polycythemia. Some causes of a high hematocrit include:

    • Dehydration—this is the most common cause of a high hematocrit. As the volume of fluid in the blood drops, the RBCs per volume of fluid artificially rises; with adequate fluid intake, the hematocrit returns to normal.
    • Lung (pulmonary) disease—if someone is unable to breathe in and absorb sufficient oxygen, the body tries to compensate by producing more red blood cells.
    • Congenital heart disease—in some forms, there is an abnormal connection between the two sides of the heart, leading to reduced oxygen levels in the blood. The body tries to compensate by producing more red blood cells.
    • Kidney tumor that produces excess erythropoietin
    • Smoking
    • Living at high altitudes (a compensation for decreased oxygen in the air)
    • Genetic causes (altered oxygen sensing, abnormality in hemoglobin oxygen release)
    • Polycythemia vera—a rare disease in which the body produces excess RBCs inappropriately
  • Is there anything else I should know?

    A recent blood transfusion will affect hematocrit results.

    Pregnancy usually causes slightly decreased hematocrit values due to extra fluid in the blood. 

  • Can my hematocrit be tested at home?
    No. This test requires instrumentation and trained laboratory personnel. A hematocrit is typically indirectly measured (i.e., calculated from RBC and MCV) by automated hematology analyzers. It can also be directly measured by spinning a blood-filled capillary tube in a centrifuge (so-called spun hematocrit), but this manual method is less commonly used.
  • Is anyone more at risk for abnormal hematocrit values? 

    Women of childbearing age tend to have lower hematocrit levels than men due to loss of iron and blood during menstrual periods and increased need for iron during pregnancy. People who have a chronic illness such as kidney disease, cancer, HIV/AIDS, chronic infection or autoimmune disorder (e.g., rheumatoid arthritis) are at risk for abnormally low hematocrit. Others who are at greater risk of a low hematocrit (anemia) include people with poor nutrition and diets low in iron or vitamins, people who have undergone surgery or people who have been severely injured. Someone who has family members with a genetic cause of anemia such as sickle cell or thalassemia also have a higher risk of having the condition and a higher risk of anemia.

View Sources

Sources Used in Current Review

Wintrobe's Clinical Hematology. 12th ed. Greer J, Foerster J, Rodgers G, Paraskevas F, Glader B, Arber D, Means R, eds. Philadelphia, PA: Lippincott Williams & Wilkins: 2009, Pp 3-4.

Harmening D. Clinical Hematology and Fundamentals of Hemostasis, Fifth Edition. F.A. Davis Company, Philadelphia, 2009, Pp 771-773.

Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. McPherson R, Pincus M, eds. Philadelphia, PA: Saunders Elsevier: 2011, Pp 512-513, 557-599.

(September 24, 2014) O'Leary M. Hematocrit. Medscape Reference. Available online at through Accessed June 2015.

Sources Used in Previous Reviews

Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].

Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.

Wu, A. (2006). Tietz Clinical Guide to Laboratory Tests, Fourth Edition. Saunders Elsevier, St. Louis, Missouri. Pp 514-517.

Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. McPherson R, Pincus M, eds. Philadelphia, PA: Saunders Elsevier: 2007, Chap 31, Pp 459-460.

Kasper DL, Braunwald E, Fauci AS, Hauser SL, Longo DL, Jameson JL eds (2005). Harrison's Principles of Internal Medicine, 16th Edition, McGraw Hill, Pp 329-336.

Pagana K, Pagana T. Mosby's Manual of Diagnostic and Laboratory Tests. 3rd Edition, St. Louis: Mosby Elsevier; 2006, Pp 296-300.

Harmening D. Clinical Hematology and Fundamentals of Hemostasis. Fifth Edition, F.A. Davis Company, Piladelphia, 2009, Pp 82-85,771-773.

(Feb 9 2010) Dugdale D. Hematocrit. MedlinePlus Medical Encyclopedia. Available online at Accessed January 2012.

(December 2005) Mayo Reference Services. How to interpret and pursue an abnormal complete blood cell count in adults. Vol. 30 No. 12. PDF available for download at through Accessed January 2012.

(March 1, 2011) National Heart, Lung and Blood Institute. What is Polycythemia vera? Available online at through Accessed Jan 2012.

(Aug 1, 2010) National Heart, Lung and Blood Institute. Anemia. Available online at through Accessed Jan 2012.

(November 4, 2011) Maarkaron J. Anemia. Medscape Reference article. Available online at through Accessed Jan 2012.

(May 26, 2011) Kahsai D. Emergent Management of Acute Anemia. Medscape Reference article. Available online at through Accessed Jan 2012.

(August 26, 2011) Harper J. Pediatric Megaloblastic Anemia. eMedicine article. Available online at through Accessed Jan 2012.

(June 8, 2011) Artz A. Anemia in Elderly Persons. eMedicine article. Available online at through Accessed Jan 2012.

Riley R, Automated Hematologic Evaluation. Medical College of Virginia, Virginia Commonwealth University. Available online at through Accessed Jan 2012.

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