Also Known As
Hgb
Hb
H and H (Hemoglobin and Hematocrit)
Formal Name
Hemoglobin
This article was last reviewed on
This article waslast modified on November 8, 2017.
At a Glance
Why Get Tested?

To evaluate the hemoglobin content of your blood as part of a general health checkup; to screen for and help diagnose conditions that affect red blood cells (RBCs); if you have anemia (low hemoglobin) or polycythemia (high hemoglobin), to assess the severity of these conditions and to monitor response to treatment

When To Get Tested?

With a hematocrit or as part of a complete blood count (CBC), which may be ordered as a component of a general health screen; when you have signs and symptoms of anemia (weakness, fatigue) or polycythemia (dizziness, headache); at regular intervals to monitor these conditions or response to 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?

None

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.

Hemoglobin Reference Range

The reference ranges 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 14-17.5 g/dL 140-175 g/L
Adult female 12.3-15.3 g/dL 123-153 g/L

1 from 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?

Hemoglobin is the iron-containing protein found in all red blood cells (RBCs) that gives the cells their characteristic red color. Hemoglobin enables RBCs to bind to oxygen in the lungs and carry it to tissues and organs throughout the body. It also helps transport a small portion of carbon dioxide, a product of cell metabolism, from tissues and organs to the lungs, where it is exhaled.

The hemoglobin test measures the amount of hemoglobin in a person's sample of blood. A hemoglobin level can be performed alone or with a hematocrit, a test that measures the proportion of blood that is made up of RBCs, to quickly evaluate an individual's red blood cells. Red blood cells, which make up about 40% (ranging 37-49%) of the blood's volume, are produced in the bone marrow and are released into the bloodstream when they are, or nearly are, mature. 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.

Several diseases and conditions can affect RBCs and consequently the level of hemoglobin in the blood. In general, the hemoglobin level and hematocrit rise when the number of red blood cells increases. The hemoglobin level and hematocrit 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. A drop in the RBC count, hemoglobin and hematocrit can result in anemia, a condition in which tissues and organs in the body do not get enough oxygen, causing fatigue and weakness. If too many RBCs are produced, polycythemia results and the blood can become thickened, causing sluggish blood flow and related problems.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm or by a fingerstick (for children and adults) or 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 hemoglobin test is often used to check for anemia, usually along with a hematocrit 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 red blood cells (RBCs) and/or the amount of hemoglobin in blood. Hemoglobin is the iron-containing protein found in all red blood cells that enables RBCs to bind to oxygen in the lungs and carry it to tissues and organs throughout the body. (For more, see the "What is being tested?" section.)

    A hemoglobin test may be used to:

    • Screen for, diagnose, and measure the severity of anemia (low RBCs, hemoglobin and hematocrit) or polycythemia (high RBCs, hemoglobin and hematocrit)
    • Monitor the response to treatment of anemia or polycythemia
    • Help make decisions about blood transfusions or other treatments if the anemia is severe

    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 through bleeding and/or the bone marrow is not able to produce new ones fast enough, then the overall number of RBCs and hemoglobin will drop, resulting in anemia.

    This test can indicate if there is a problem with red blood cell production and/or lifespan, 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 hemoglobin test may be ordered during a general health examination or when a person has signs and symptoms of a condition affecting red blood cells such as anemia or 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

    This test may be performed several times or on a regular basis when someone has been diagnosed with ongoing bleeding problems or chronic anemias 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?

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

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

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

    • 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 tumors that produce excess erythropoietin
    • Smoking—heavy smokers have higher hemoglobin levels than nonsmokers.
    • Genetic causes (altered oxygen sensing, abnormality in hemoglobin oxygen release)
    • Living at high altitudes (a compensation for decreased oxygen in the air)
    • Dehydration—as the volume of fluid in the blood drops, the hemoglobin artificially rises.
    • Polycythemia vera—a rare disease in which the body produces excess RBCs inappropriately
  • Is there anything else I should know?

    A recent blood transfusion can affect a person's hemoglobin level.

    Hemoglobin decreases slightly during normal pregnancy

  • Can I test my hemoglobin at home?

    Yes, there are some home tests currently available that have been approved by the U.S. Food and Drug Administration (FDA). Home testing offers many benefits, but it's also important to recognize the potential tradeoffs between quality and convenience and to take steps to protect yourself against the possibility of false results, and your own lack of training. Talk to your doctor about this type of testing and consult her about any questions or concerns you may have. For more about these tests, see the article With Home Testing, Consumers Take Charge of Their Health.

  • Is anyone at greater risk of abnormal hemoglobin levels?

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

  • Are there warning signs for abnormally low hemoglobin levels?

    Some warning signs are fatigue, fainting, pale skin (pallor), and shortness of breath.

  • Can a healthy diet and nutrition help keep optimal hemoglobin levels?

    Yes, to the extent that if you eat a well-balanced diet, you can prevent anemia due to a lack of iron, vitamin B12, or folate in the foods you eat. Sometimes use of a supplement is recommended if you are at risk of a vitamin deficiency. However, the most common cause of vitamin B12 deficiency is malabsorption, and the most common cause of iron deficiency is bleeding. These conditions and other red blood cell problems that are caused by diseases other than nutritional deficiencies cannot be corrected by diet.

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, Pg 4.

Harmening D, Clinical Hematology and Fundamentals of Hemostasis, Fifth Edition, F.A. Davis Company, Philadelphia, 2009, Pp 70, 771.

Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. McPherson R, Pincus M, eds. Philadelphia, PA: Saunders Elsevier: 2011, 510-512, 557-599.

(Updated February 12, 2014) Yang B. Hemoglobin Concentration. Medscape Reference. Available online at http://emedicine.medscape.com/article/2085614-overview#a4 through http://emedicine.medscape.com. 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 524-527.

Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. McPherson R, Pincus M, eds. Philadelphia, PA: Saunders Elsevier: 2007, Chap 31, Pp 458, 489-491.

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 300-303.

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

(Feb 9 2010) Dugdale D. Hemoglobin. MedlinePlus Medical Encyclopedia. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003645.htm. 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 http://www.mayomedicallaboratories.com/media/articles/communique/mc2831-1205.pdf through http://www.mayomedicallaboratories.com. Accessed January 2012.

(March 1, 2011) National Heart, Lung and Blood Institute. What is Polycythemia vera? Available online at http://www.nhlbi.nih.gov/health/public/blood/index.htm through http://www.nhlbi.nih.gov. Accessed Jan 2012.

(Aug 1, 2010) National Heart, Lung and Blood Institute. Anemia. Available online at http://www.nhlbi.nih.gov/health/health-topics/topics/anemia/ through http://www.nhlbi.nih.gov. Accessed Jan 2012.

(November 4, 2011) Maarkaron J. Anemia. Medscape Reference article. Available online at http://emedicine.medscape.com/article/198475-overview through http://emedicine.medscape.com. Accessed Jan 2012.

(May 26, 2011) Kahsai D. Emergent Management of Acute Anemia. Medscape Reference article. Available online at http://emedicine.medscape.com/article/780334-overview#a1 through http://emedicine.medscape.com. Accessed Jan 2012.

(August 26, 2011) Harper J. Pediatric Megaloblastic Anemia. eMedicine article. Available online at http://emedicine.medscape.com/article/959918-overview through http://emedicine.medscape.com. Accessed Jan 2012.

(June 8, 2011) Artz A. Anemia in Elderly Persons. eMedicine article. Available online at http://emedicine.medscape.com/article/1339998-overview through http://emedicine.medscape.com. Accessed Jan 2012.

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