What is hemoglobin?

What is hemoglobin?

Hemoglobin is the protein molecule in red blood cells that carries oxygen from the lungs to the body's tissues and returns carbon dioxide from the tissues to the lungs.

Hemoglobin is made up of four protein molecules (globulin chains) that are connected together. The normal adult hemoglobin (Hbg) molecule contains 2 alpha-globulin chains and 2 beta-globulin chains. In fetuses and infants, there are only a few beta chains and the hemoglobin molecule is made up of 2 alpha chains and 2 gamma chains. As the infant grows, the gamma chains are gradually replaced by beta chains.

Each globulin chain contains an important central structure called the heme molecule. Embedded within the heme molecule is iron that transports the oxygen and carbon dioxide in our blood. The iron contained in hemoglobin is also responsible for the red color of blood.

Hemoglobin also plays an important role in maintaining the shape of the red blood cells. Abnormal hemoglobin structure can, therefore, disrupt the shape of red blood cells and impede its function and its flow through blood vessels.

How is hemoglobin measured?

Hemoglobin is usually measured as a part of the complete blood count (CBC) from a blood sample.

Several methods exist for measuring hemoglobin, most of which are done currently by automated machines designed to perform several different tests on blood. Within the machine, the red blood cells are broken down to get the hemoglobin into a solution. The free hemoglobin is exposed to a chemical containing cyanide which binds tightly with the hemoglobin molecule to form cyanmethemoglobin. By shining a light through the solution and measuring how much light is absorbed (specifically at a wavelength of 540 nanometers), the amount of hemoglobin can be determined.

What are normal hemoglobin values?

The hemoglobin level is expressed as the amount of hemoglobin in grams (gm) per deciliter (dl) of whole blood, a deciliter being 100 milliliters.

The normal ranges for hemoglobin depend on the age and, beginning in adolescence, the gender of the person. The normal ranges are:

• Newborns: 17-22 gm/dl
• One (1) week of age: 15-20 gm/dl
• One (1) month of age: 11-15gm/dl
• Children: 11-13 gm/dl
• Adult males: 14-18 gm/dl
• Adult women: 12-16 gm/dl
• Men after middle age: 12.4-14.9 gm/dl
• Women after middle age: 11.7-13.8 gm/dl

All of these values may vary slightly between laboratories. Some laboratories do not differentiate between adult and "after middle age" hemoglobin values.

What does a low hemoglobin level mean?

A low hemoglobin is referred to as anemia. There are many reasons for anemia.

Some of the more common causes are:

• loss of blood (traumatic injury, surgery, bleeding colon cancer or stomach ulcer),
• nutritional deficiency (iron, vitamin B12, folate),
• bone marrow problems (replacement of bone marrow by cancer,
• suppression by chemotherapy drugs,
• kidney failure), and
• abnormal hemoglobin (sickle cell anemia).

What does a high hemoglobin level mean?

Higher than normal hemoglobin levels can be seen in people living at high altitudes and in people who smoker. Dehydration produces a falsely high hemoglobin which disappears when proper fluid balance is restored.

Some other infrequent causes are:

• advanced lung disease (for example, emphysema),
• certain tumors,
• a disorder of the bone marrow known as polycythemia rubra vera, and
• abuse of the drug erythropoietin (Epogen) by athletes for blood doping purposes.

What is sickle cell disease?

Sickle cell disease is a genetic condition in which the quality of hemoglobin is defective. This condition can cause abnormal hemoglobin which, in turn, can result in abnormally shaped (sickled) red blood cells. These abnormal red blood cells cannot easily pass through small blood vessels and, therefore, could deprive the body organs of adequate oxygen.

Sickle cells also have a shorter life span than normal red blood cells (10-20 days compared to 120 days). This rapid turn over may result in inadequate time to replace the red blood cells and may result in anemia.

In order for a person to have sickle cell anemia, one defective hemoglobin gene must be inherited from each parent. If only one gene is inherited from one parent, then the conditions is much milder and it is referred to as sickle cell trait.