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:

• Symptoms such as fatigue, poor health, or unexplained weight loss
• Signs of bleeding
• Before and after major surgery
• During pregnancy
• Chronic kidney disease or many other chronic medical problems
• Monitoring of anemia and its cause
• Monitoring during treatment for cancer
• Monitoring medicines that may cause anemia or low blood counts

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 caused by red blood cells dying earlier than normal (hemolytic anemia)
• Anemia (various types)
• Bleeding from digestive tract or bladder, heavy menstrual periods
• Chronic kidney disease
• 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
• Poor nutrition (including low level of iron, folate, vitamin B12, or vitamin B6)
• Low level of iron, folate, vitamin B12, or vitamin B6
• Other chronic illness, such as rheumatoid arthritis

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:

• Certain birth defects of the heart that are present at birth (congenital heart disease)
• Failure of the right side of the heart (cor pulmonale)
• Severe chronic obstructive pulmonary disease (COPD)
• Scarring or thickening of the lungs (pulmonary fibrosis) and other severe lung disorders

Other reasons for high hemoglobin level includes:

• A rare bone marrow disease that leads to an abnormal increase in the number of blood cells (polycythemia vera)
• The body having too little water and fluids (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

Bunn HF. Approach to the anemias In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 158.

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.