Hemoglobin

Alternative names:

Hb; Hgb

What the risks are:

• excessive bleeding
• fainting or feeling lightheaded
• hematoma (blood accumulating under the skin)
• infection (a slight risk any time the skin is broken)
• multiple punctures to locate veins

Special considerations:

Hemoglobin (Hb), the main component of red blood cells, is a protein that carries oxygen away from the lungs and CO2 back to the lungs. A molecule of hemoglobin consists of 2 pairs of peptide (alpha and beta globins) chains and 4 heme groups, each with 1 atom of ferrous iron. At an oxygen tension (pressure) of 100 mmHg in the pulmonary (lung) capillaries, 95 to 98% of the Hb is combined with oxygen. In the peripheral tissues, where the oxygen tension may be as low as 20 mmHg, the oxygen readily dissociated from Hb and less than 30% of the oxygen remains combined with Hb. (See also serum hemoglobin.)

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.