A hemoglobin test measures the amount of hemoglobin in the blood. Hemoglobin is a protein in red blood cells that transports oxygen to the organs and tissues of the body and carbon dioxide from them back to the lungs.

If a hemoglobin test shows that your hemoglobin level is lower than normal, it means you have a low red blood cell count (anemia). Anemia can have many different causes, including vitamin deficiencies, bleeding, and chronic disease.

If the hemoglobin test shows higher than normal levels, there are several potential causes -- the blood disorder polycythemia vera, living at high altitudes, smoking, and dehydration.

Normal Results of Hemoglobin

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 above ranges are common measurements for these test results. Different laboratories may have slightly different ranges of normal values. Some labs use different measurements or test different samples. Discuss the meaning of your specific test results with your healthcare provider.

Lower than normal Hemoglobin

Low hemoglobin levels may be due to:

• anemia

• bleeding

• The bone marrow cannot produce new red blood cells. This may be due to leukemia, other cancers, drug toxicity, radiation therapy, infection, or bone marrow disease

• chronic illness

• chronic kidney disease

• Destruction of red blood cells (hemolysis)

• leukemia

• Malnutrition

• Too little iron, folic acid, vitamin B12, and vitamin B6 in your diet

• excessive body water

Higher than normal Hemoglobin

The most common cause of high hemoglobin levels is chronically low levels of oxygen in the blood (hypoxia). Common causes include:

• A bone marrow disorder that causes an abnormal increase in red blood cells (polycythemia vera)

• congenital heart disease

• exposure to high altitude

• right heart failure

• low oxygen levels in the blood

• scarring or thickening of the lungs

• Too little body water (dehydration)