What is Hemoglobin?

What's in this article?

1 How is hemoglobin test measured?
2 What does low hemoglobin mean?
3 What does high hemoglobin mean?

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 back to the lungs.

Hemoglobin is made up of four protein molecules (globulin chains) that are connected together. The normal adult hemoglobin (abbreviated Hgb or Hb) molecule contains two alpha-globulin chains and two beta-globulin chains. In fetuses and infants, beta chains are not common and the hemoglobin molecule is made up of two alpha chains and two gamma chains. As the infant grows, the gamma chains are gradually replaced by beta chains, forming the adult hemoglobin structure.

Each globulin chain contains an important iron-containing porphyrin compound termed heme. Embedded within the heme compound is an iron atom that is vital in transporting 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. In their natural shape, red blood cells are round with narrow centers resembling a donut without a hole in the middle. Abnormal hemoglobin structure can, therefore, disrupt the shape of red blood cells and impede their function and flow through blood vessels.

How is hemoglobin test measured?

Hemoglobin is routinely measured as part of a routine blood test termed blood count (CBC). A complete blood count is one of the most common tests doctors order for a patient. It is done on automated machines that use a blood sample that is chemically treated to release hemoglobin from red blood cells. The released hemoglobin then is bound chemically to cyanide that forms a compound that absorbs light. The amount of absorbed light is then measured, and this measurement is directly related to how much hemoglobin is present in the blood.

What does low hemoglobin mean?

Low hemoglobin means that a person’s hemoglobin level when measured, is below the lowest limits of normal for their age and sex (see above normal range of values). For example, a 19 year old male would have low hemoglobin if the detected blood value was below 13.6 g/dl. Another term frequently used in place of low hemoglobin is anemia, or the person is described as being anemic. Some of the more common causes of anemia are as follows:

Nutritional (iron, folic acid, or vitamin B 12 deficiency [pernicious anemia])
Gastrointestinal blood loss (ulcers,colon cancer)
Kidney problems
Blood loss (from trauma or surgery)
Red Blood cell synthesis problems (bone marrow disorders, genetic disorders such as sickle cell anemia)
Bone marrow suppression by chemotherapy or radiation exposure

What does high hemoglobin mean?

High hemoglobin levels mean that measured hemoglobin levels are above th e upper limits of normal for the age and sex of the person (see above normal values). For example, a 19 year old that has a detected hemoglobin level of above 17.7 g/dl would have a high hemoglobin level. Some causes for high hemoglobin levels are as follows: