Health Encyclopedia

Hemoglobin

Definition

Hemoglobin is a protein in red blood cells that carries oxygen. The hemoglobin test measures how much hemoglobin is in your blood.

Alternative Names

Hgb; Hb; Anemia - Hb; Polycythemia - Hb

How the Test is Performed

A blood sample is needed.

How to Prepare for the Test

No special preparation is necessary.

How the Test will Feel

When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or a slight bruise. This soon goes away.

Why the Test is Performed

The hemoglobin test is a common test and is almost always done as part of a complete blood count (CBC). Reasons or conditions for ordering the hemoglobin test include:

Before and after major surgery
Blood in your stools, or vomit (if you throw up)
Chronic medical problems, such as kidney disease or certain types of arthritis
During pregnancy
Fatigue, poor health, or unexplained weight loss
Headaches
Heavy menstrual periods
Leukemia or other problems in the bone marrow
Monitoring during treatment for cancer
Monitoring medicines that may cause anemia or low blood counts
Monitoring of anemia and its cause
Poor nutrition
Problems concentrating

Normal Results

Normal results for adults vary, but in general are:

Male: 13.8 to 17.2 grams per deciliter (g/dL) or 138 to 172 grams per liter (g/L)
Female: 12.1 to 15.1 g/dL or 121 to 151 g/L

Normal results for children vary, but in general are:

Newborn: 14 to 24 g/dL or 140 to 240 g/L
Infant: 9.5 to 13 g/dL or 95 to 130 g/L

The ranges above are common measurements for results of these tests. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your health care provider about the meaning of your specific test results.

What Abnormal Results Mean

LOWER THAN NORMAL HEMOGLOBIN

Low hemoglobin level may be due to:

Anemia
Bleeding
Bone marrow being unable to produce new red blood cells. This may be due to leukemia, other cancers, drug toxicity, radiation therapy, infection, or bone marrow disorders
Chronic illness
Chronic kidney disease
Destruction of red blood cells (hemolysis)
Leukemia
Malnutrition
Too little iron, folate, vitamin B12, and vitamin B6 in the diet
Too much water in the body

HIGHER THAN NORMAL HEMOGLOBIN

High hemoglobin level is most often caused by low oxygen levels in the blood (hypoxia), present over a long period of time. Common reasons include:

Bone marrow disease that causes abnormal increase in red blood cells (polycythemia vera)
Congenital heart disease
Exposure to high altitude
Failure of the right side of the heart
Low levels of oxygen in the blood
Scarring or thickening of the lungs
Too little water in the body (dehydration)

Risks

There is little risk involved with having your blood taken. Veins and arteries vary in size from one person to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight, but may include:

Excessive bleeding
Fainting or feeling lightheaded
Multiple punctures to locate veins
Hematoma (blood buildup under the skin)
Infection (a slight risk any time the skin is broken)

References

Chernecky CC, Berger BJ. Hemoglobin (HB, Hgb). In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures. 6th ed. Philadelphia, PA: Elsevier; 2013:621-623.

Marcdante KJ, Kliegman RM, Schuh AM. Hematology assessment. In: Marcdante KJ, Kliegman RM, Schuch AM, eds. Nelson Essentials of Pediatrics. 9th ed. Elsevier; 2023:chap 149.

Means RT. Approach to the anemias. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 149.

Review Date:1/9/2022
Reviewed By:David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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