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

Hgb; Hb

A blood sample is needed.

No special preparation is necessary.

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.

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

• Symptoms such as fatigue, feelings of poor health, or unexplained weight loss
• Signs of bleeding are present
• Before and after major surgery
• During pregnancy
• Presence of 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 for adults vary, but in general are:

• Male: 13.8 to 17.2 grams per deciliter (g/dL)
• Female: 12.1 to 15.1 g/dL

Normal results for children vary, but in general are:

• Newborn: 14 to 24 g/dL
• Infant: 9.5 to 13 g/dL

The examples 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 doctor about the meaning of your specific test results.

LOWER THAN NORMAL HEMOGLOBIN

Low hemoglobin level may be due to:

• Anemia due to red blood cells being destroyed 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 blood cells. This may be due to leukemia, other cancers, drug toxicity, radiation therapy, infection, or bone marrow disorders
• Poor nutrition
• 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 due to low oxygen levels in the blood (hypoxia), present over a long period of time. Common reasons include:

• Certain birth defects of the heart, present at birth (congenital heart disease)
• Failure of the right side of the heart (cor pulmonale)
• Severe 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 not having as much water and fluids as it should (dehydration)

Veins and arteries vary in size from one patient 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 light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

Hutchison RE, McPherson RA, Schexneider KI. Basic examination of blood and bone marrow. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, Pa: Elsevier Saunders; 2011:chap 30.