Hemoglobin is the iron-containing protein found in all red blood cells (RBCs) that gives the cells their characteristic red color. Hemoglobin enables RBCs to bind to oxygen in the lungs and carry it to tissues and organs throughout the body. It also helps transport a small portion of carbon dioxide, a product of cell metabolism, from tissues and organs to the lungs, where it is exhaled.
The hemoglobin test measures the amount of hemoglobin in a person's sample of blood. A hemoglobin level can be performed alone or with a hematocrit, a test that measures the proportion of blood that is made up of RBCs, to quickly evaluate an individual's red blood cells. Red blood cells, which make up about 40% (ranging 37-49%) of the blood's volume, are produced in the bone marrow and are released into the bloodstream when they are, or nearly are, mature. The typical lifespan of an RBC is 120 days, and the bone marrow must continually produce new RBCs to replace those that age and degrade or are lost through bleeding.
Several diseases and conditions can affect RBCs and consequently the level of hemoglobin in the blood. In general, the hemoglobin level and hematocrit rise when the number of red blood cells increases. The hemoglobin level and hematocrit fall to less than normal when there is a drop in production of RBCs by the bone marrow, an increase in the destruction of RBCs, or if blood is lost due to bleeding. A drop in the RBC count, hemoglobin and hematocrit can result in anemia, a condition in which tissues and organs in the body do not get enough oxygen, causing fatigue and weakness. If too many RBCs are produced, polycythemia results and the blood can become thickened, causing sluggish blood flow and related problems.
Hgb; Hb; H and H (Hemoglobin and Hematocrit); Hemoglobin.
To evaluate the hemoglobin content of your blood as part of a general health checkup; to screen for and help diagnose conditions that affect red blood cells (RBCs); if you have anemia (low hemoglobin) or polycythemia (high hemoglobin), to assess the severity of these conditions and to monitor response to treatment. With a hematocrit or as part of a complete blood count (CBC), which may be ordered as a component of a general health screen; when you have signs and symptoms of anemia (weakness, fatigue) or polycythemia (dizziness, headache); at regular intervals to monitor these conditions or response to treatment.
The hemoglobin test may be ordered during a general health examination or when a person has signs and symptoms of a condition affecting red blood cells such as anemia or polycythemia.
Some signs and symptoms of anemia include:
Weakness or fatigue
Lack of energy
Shortness of breath
Some signs and symptoms of polycythemia include:
This test may be performed several times or on a regular basis when someone has been diagnosed with ongoing bleeding problems or chronic anemias or polycythemia to determine the effectiveness of treatment. It may also be ordered routinely for people undergoing treatment for cancer that is known to affect the bone marrow.