Hemoglobin is a molecule comprised of four subunits. Each subunit contains an iron containing pigment (heme) and a protein (globulin). There are two types of subunits, alpha and beta. Each gram of hemoglobin can carry 1.34 ml of oxygen. The oxygen carrying ability of blood is directly proportional to its hemoglobin concentration. The numbers of red blood cells does not indicate blood's oxygen content because some cells may contain more hemoglobin than others. Hemoglobin determination is used to screen for anemia, to identify the severity of anemia, and to assist in evaluating the patient's response to anemia therapy. Hemoglobin also serves as an important pH buffer in the extracellular fluid.
Glucose irreversibly attaches to hemoblobin and other proteins that it contacts. Measurement of hemoglobin A-1C or glycosylated hemoglobin is used to monitor and evaluate diabetes. The amount of hemoglobin A-1C reflects an average blood glucose over a 3 month period, compared to a fasting blood glucose that reflects blood glucose during a one-time fasting state. Adult non-diabetics have a hemoglobin A-1C value between 2% and 5%. Diabetics with effective disease control have hemoglobin A-1C values between 2.5% and 6%. Diabetics with poor disease
control may have values of 8% and higher.
Blood loss and bone marrow suppression reduce total RBC count and therefore lower total hemoglobin content. Hemoglobin levels are also lowered in patients who have abnormal types of hemoglobin or hemoglobinopathies. Red blood cells with abnormal types of hemoglobin are often fragile and damaged or destroyed easily in the vascular system. Hemoglobin electrophoresis can distinguish among specific types of abnormal hemoglobin.
Thalassemia is an inherited recessive hemoglobinopathy. It results from a failure to produce sufficient globin molecules. The failure can be in either the alpha or beta portion. In sickle cell anemia, the patient has an abnormally shaped hemoglobin known as sickle hemoglobin (hgbS). Sickle hemoglobin creates misshapen RBCs which form blockages in the vessels.
Other patients have a normal RBC count but a low hemoglobin level. This situation occurs with iron-deficiency anemia, in which red blood cells have less hemoglobin than normal. Iron deficiency anemia is also referred to as hypochromic anemia. Hypochromic is a term that means "less than normal color." In general, women need more iron in their diets than men, due to the regular loss of iron in the menstrual flow. During pregnancy a woman's need for iron to build more hemoglobin increases. If a woman becomes pregnant when she has low iron reserves, she is at risk of becoming severely anemic. Regular hemoglobin testing is an important part of prenatal care. During the last trimester of pregnancy, a condition known as "physiological anemia of pregnancy" occurs. This normal drop in hemoglobin values results from an increase in the plasma volume. Multiple blood draws in premature infants is a common cause of anemia.
Hemoglobin: critical low and high values
Increased levels of hemoglobin are found in any condition in which the number of circulating red blood cells rises above normal. Examples of conditions associated with increases in hemoglobin are polycythemia vera , severe burns, chronic obstructive pulmonary disease, and congestive heart failure.
For more information about anemia, consider visiting the AMERICAN SOCIETY of HEMATOLOGY website
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