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Alternative names Return to top
Hgb; HbDefinition Return to top
A hemoglobin test measures the total amount of hemoglobin in the blood. Hemoglobin is almost always ordered as part of a complete blood count (CBC). See also Hemoglobin electrophoresis.How the test is performed Return to top
Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins to fill with blood.
A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
In infants or young children:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.
How to prepare for the test Return to top
No special preparation is necessary.How the test will feel Return to top
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.Why the test is performed Return to top
Hemoglobin is the protein that carries oxygen in the blood. It is contained in red blood cells. Both high and low hemoglobin counts indicate defects in the balance of red blood cells in the blood, and may indicate disease.Normal Values Return to top
Hemoglobin (varies with altitude):What abnormal results mean Return to top
Lower-than-normal hemoglobin may indicate:What the risks are Return to top
Special considerations Return to top
Hemoglobin (Hb), the main component of red blood cells, is a protein that carries oxygen from the lungs to the body's tissues, and carbon dioxide from the tissues to the lungs to be exhaled.
At a pressure of 100 mmHg in the lung's capillaries, 95-98% of the Hb is combined with oxygen. In the peripheral tissues, where the pressure may be as low as 20 mmHg, 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.
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Page last updated: 28 October 2004 |