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.

A hemoglobin test reveals how much hemoglobin is in a person's blood. This information can be used to help physician's diagnose and monitor anemia (a low hemoglobin level) and polycythemia vera (a high hemoglobin level).

How is measure for hemoglobin?
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.

The RBCs in the sample of blood are packed down by spinning the tube in a centrifuge under prescribed conditions. The proportion of the tube that consists of RBCs is then measured. Let's say that it is 45%. The hematocrit is 45.

What are normal hemoglobin values?
Normal values vary with age and sex, with women generally having lower hemoglobin values than men. Normal results for men range from 13–18 g/dL. For women the normal range is 12–16 g/dL. Critical limits (panic values) for both males and females are below 5.0 g/dL or above 20.0 g/dL.

What does a low hemoglobin level mean?
A low hemoglobin is referred to as being anemic. There are many reasons for anemia. Some of the more common reasons are loss of blood (traumatic injury, surgery, bleeding colon cancer), 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 smokers. Dehydration produces a falsely high hemoglobin which disappears when proper fluid balance is restored. Some other infrequent causes are lung disease, 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.

Which are additional conditions that the hemoglobin test will be performed:

• Anemia of chronic disease
• Clinical hemoglobin C
• Diabetes
• Giant cell arteritis
• Aplastic anemia
• Hemolytic anemia
• Iron deficiency anemia
• Paroxysmal cold hemoglobinuria (PCH)
• Paroxysmal nocturnal hemoglobinuria (PNH)
• Pernicious anemia
• Placenta abruptio
• Polymyalgia rheumatica
• Rhabdomyolysis