Definition of Hemoglobin and Importance in the Body

Why Is Hemoglobin Important and When Is it a Problem?

diagram of red blood cells
What is hemoglobin and why is it important?. Wikimedia Commons/Egelberg

Definition: Hemoglobin

Hemoglobin is a protein in red blood cells (RBCs) that carries oxygen from the lungs to the tissues in the body. The pigment in hemoglobin is responsible for the red color of blood.

Structure of Hemoglobin

Hemoglobin is protein in red blood cells that is made up of four chains. Each of these chains contains a compound known as heme, which in turn contains iron, which is what transports oxygen in the blood stream.

Hemoglobin is responsible for the shape of red blood cells, which usually appear like donuts but with a thin center rather than a hole. In conditions in which hemoglobin is abnormal, such as sickle cell anemia, the consequent abnormal shape of the red blood cells can lead to problems.


Hemoglobin,as noted above, transports oxygen from the capillaries in the lungs to all of the tissues in the body.

Normal Range

A hemoglobin is usually checked as a part of a complete blood count (CBC), The normal range of hemoglobin varies depending upon on age and sex. The average range is 14-18 g/dl for an adult male and 12-16 g/dl for an adult female.

Conditions with a Low Hemoglobin

A low hemoglobin level is referred to as anemia   Causes of anemia may include anything which interferes either with hemoglobin, or the number of red blood cells present in the body. With red blood cells, in turn, there may be a loss (as in bleeding) a lack of production in the bone marrow or the red blood cells may instead be broken down in the bloodstream ("hemolyzed.) There are many causes of a low hemoglobin including:

  • Blood loss - This may occur due to surgery, heavy menstrual periods, blood loss from the gastrointestinal tract, or any other form of bleeding.
  • Lack of production in the bone marrow, either due to bone marrow failure, or infiltration of the bone marrow with cancer.
  • Breakdown of red blood cells, as in hemolytic anemia.
  • Nutritional deficiency or due to an inadequate intake of iron (iron deficiency anemia) or vitamin B12.
  • Kidney disease.

Conditions with an Elevated Hemoglobin

There are several conditions associated with an elevated level of hemoglobin as well, including:

  • Lung diseases such as COPD and pulmonary fibrosis.
  • Congenital heart disease (heart disease that is present at birth.)
  • Right heart failure (cor pulmonale.)
  • The hemoglobin level may be artificially elevated (only appear to be elevated) due to dehydration.

Abnormal Hemoglobins

Conditions in which hemoglobin has an abnormal structure include:

  • Sickle cell anemia - Sickle cell anemia is an inherited condition in which the abnormal hemoglobin results in red blood cells which are shaped like sickles. These red blood cells can get "stuck" in blood vessels resulting in a number of problems.
  • Thalassemia  


Treatments of an abnormal hemoglobin level depend on the underlying cause of an elevated or decreased count. Blood transfusions may be used to quickly increase red blood cells/hemoglobin in the body.  In cases where anemia exists due to a lack of red blood cell production, the medication Epogen (erythropoietin) is sometimes used to stimulate the formation of red blood cells.

Hemoglobin A1c or Glycosylated Hemoglobin

You may hear of the blood test hemoglobin A1c which is drawn to monitor diabetes. This test can reflect the level of blood sugar in a person's body over a period of months based on how much glucose is attached to hemoglobin.

Examples: Frank was feeling tired after chemotherapy, and his oncologist told him his hemoglobin was low.


National Library of Health. MedlinePlus. Hemoglobin. Updated 01/31/16.

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