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 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 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.

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
• Pregnancy
• 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 RBCs (polycythemia vera)
• Cigarette smoking
• Dehydration (for example, from severe diarrhea)
• Failure of the right side of the heart (cor pulmonale)
• Kidney tumor (renal cell carcinoma)
• Low blood oxygen level (hypoxia)
• Problem with heart's structure and function that is present at birth (congenital heart disease)
• Scarring or thickening of the lungs (pulmonary fibrosis)

Your hemoglobin level will increase for several weeks when you are in a higher altitude.

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)

Hgb; Hb; Anemia - Hb; Polycythemia - Hb

Kliegman RM, St. Geme JW, Blum NJ, Shah SS, Tasker RC, Wilson KM. Blood disorders. In: Kliegman RM, St. Geme JW, Blum NJ, Shah SS, Tasker RC, Wilson KM, eds. Nelson Textbook of Pediatrics. 21st ed. Philadelphia, PA: Elsevier; 2020:chap 124.

Means RT Jr. Approach to the anemias. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 144.

Vajpayee Neerja, Graham SS, Bem S. Basic examination of blood and bone marrow. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 31.

Updated by: Frank D. Brodkey, MD, FCCM, Associate Professor, Section of Pulmonary and Critical Care Medicine, University of Wisconsin School of Medicine and Public Health, Madison, WI. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.