Hemoglobin

Alternate Names
serum hemoglobin
total hemoglobin

Definition of Hemoglobin

Hemoglobin is a complex molecule found in red blood cells. Part of the molecule is protein and the other part, known as a porphyrin, contains an iron atom which can bind and carry oxygen. The iron in hemoglobin is responsible for the red color of blood. Hemoglobin carries oxygen from the lungs to cells throughout the body, then returns carbon dioxide from the cells to the lungs to be exhaled. A hemoglobin test measures the level of this protein in a sample of blood.

Who is a candidate for the test?

Often, this test is part of a complete blood count (CBC). It may also be done:

• during pregnancy
• during infancy
• when a person has symptoms of anemia, such as lack of energy, pale skin, and shortness of breath
• to measure progress when a person is being treated for anemia
• when family history or ethnic or racial background puts a person at risk for a blood disorder, such as sickle cell disease or thalassemia.

How is the test performed?

Blood for the test is usually taken from a person's forearm. First, a tight band is put on the upper arm to make the veins swell below it. An area of skin on the forearm over the vein chosen is cleansed.

A needle is inserted into the vein and a sample of blood is collected in a tube. Occasionally blood is taken from another site, such as a finger or heel. If so, the skin is cleansed and pricked with a sharp tool called a lancet. Drops of blood are collected in a tiny tube and analyzed in a laboratory.

What is involved in preparation for the test?

Generally, no preparation is needed.

What do the test results mean?

Age, sex, and other factors cause normal ranges for hemoglobin to vary. Generally, healthy test ranges are:

• newborns - 14 to 20 grams of hemoglobin per deciliter of blood (g/dl)
• children 6 months to 6 years -- 9.5-14 g/dl
• children 6 to 18 years - 10 to 15.5 g/dl
• men 18 or older - 14 to 18 g/dl
• women 18 or older -12 to 16 g/dl
• pregnant women -- at least 11 g/dl

A low hemoglobin level generally means that a person's overall supply of red cells is low, a condition known as anemia.

The many common causes of anemia include:

• excessive menstrual bleeding in women
• gastrointestinal bleeding, such as that from bleeding peptic ulcers and colon cancer
• malnutrition
• increased nutritional needs, which occurs during rapid growth periods of childhood and in pregnancy
• inherited causes, such as sickle cell disease, a condition in which red cells are misshaped because of an abnormal hemoglobin molecule

An increased hemoglobin level can occur for several reasons. Common causes include:

• dehydration. The hemoglobin concentration is high in the blood sample simply because the person has lost blood fluid volume. The hemoglobin value will normalize once the person is re-hydrated.
• chronic obstructive pulmonary diseases, such as emphysema, which is usually due to smoking cigarettes
• blood cancer, such as a cancer called polycythemia vera

Depending on the result of this test and its suspected cause, the healthcare professional may recommend treatment or further testing.