Hemoglobin Importance Within the Body

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

What is the definition of hemoglobin? What are normal levels and when is the number high or low? What does it mean if you have an abnormal hemoglobin level and what tests may be done? You may be surprised at the number of different conditions which can affect your hemoglobin level.


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.


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 bloodstream.

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 functions by binding and transporting oxygen from the capillaries in the lungs to all of the tissues in the body.

Normal Range 

A hemoglobin level 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 (either due to damage to the bone marrow or the replacement of marrow by tumor cells,) or the red blood cells may instead be broken down in the bloodstream ("hemolyzed.") There are many possible 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. Women who are premenopausal are much more likely than men to have a low hemoglobin level due to the monthly loss of blood.
  • Lack of production in the bone marrow, either due to bone marrow failure (such as aplastic anemia,) or infiltration of the bone marrow with cancer (such as with leukemias or lymphomas or solid tumors such as metastatic breast cancer.)
  • Breakdown of red blood cells, as in hemolytic anemia.
  • Nutritional deficiency or inadequate intake of iron (iron deficiency anemia) or vitamin B12 (pernicious anemia.)
  • 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  

Other Tests to Evaluate Hemoglobin Levels

When a doctor notes a low hemoglobin level she also looks at other lab tests which may help to determine the cause. These include the total red blood cell count, red blood cell indices such as MCHC (mean corpuscular hemoglobin concentration,) MCH (mean corpuscular hemoglobin,) and MCV (mean corpuscular volume.) A serum ferritin level may also be done which provides an indication of iron stores in the body.

Bottom Line

If you hear about hemoglobin, you may think of bleeding, especially heavy menstrual bleeding. Yet there is a wide range of disorders that can result in either an elevated or decreased hemoglobin. In addition, there are abnormal types of hemoglobin which can contribute to disease. In order to determine a cause of a low or high hemoglobin, your doctor will ask questions, perform a physical exam, and look at other blood tests in combination with your hemoglobin level.

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

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