Hemoglobin A1c (HbA1c) Glossary of Terms

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A1C: A test that measures how much glucose has been sticking during the past 3-4 months to hemoglobin, the substance in the red blood cells that carries oxygen to the cells of the body. The A1C test is important in diabetes as a long-term measure of control over blood glucose. Even outside of diabetes, an elevated A1C level may be a cardiovascular risk factor.
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Acute: Of abrupt onset, in reference to a disease. Acute often also connotes an illness that is of short duration, rapidly progressive, and in need of urgent care.
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Blood glucose: The main sugar that the body makes from the food in the diet. Glucose is carried through the bloodstream to provide energy to all cells in the body. Cells cannot use glucose without the help of insulin.
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Cell: The basic structural and functional unit in people and all living things. Each cell is a small container of chemicals and water wrapped in a membrane.
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Chronic: This important term in medicine comes from the Greek chronos, time and means lasting a long time.
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Diabetes: Refers to diabetes mellitus or, less often, to diabetes insipidus. Diabetes mellitus and diabetes insipidus share the name "diabetes" because they are both conditions characterized by excessive urination (polyuria).
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Fasting: going without food or drink. Patients may be advised to fast for a certain period of time prior to surgery, medical procedures, or certain blood tests.

Fasting blood glucose: A method for learning how much glucose (sugar) there is in a blood sample taken after an overnight fast. The fasting blood glucose test is commonly used in the detection of diabetes mellitus. A blood sample is taken in a lab, doctor's office, or hospital. The test is done in the morning before the person has eaten. The normal, nondiabetic range for blood glucose is from 70 to 110 mg/dl, depending on the type of blood being tested. If the level is over 140 mg/dl, it usually means the person has diabetes (except for newborns and some pregnant women).

Glucose: The simple sugar (monosaccharide) that serves as the chief source of energy in the body. Glucose is the principal sugar the body makes. The body makes glucose from proteins, fats and, in largest part, carbohydrates. Glucose is carried to each cell through the bloodstream. Cells, however, cannot use glucose without the help of insulin. Glucose is also known as dextrose.
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Glycohemoglobin: Also known as glycosylated hemoglobin, hemoglobin to which glucose is bound, a measure of the long-term control of diabetes mellitus.
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Glycosylated hemoglobin: Hemoglobin to which glucose is bound. Glycosylated hemoglobin is tested to monitor the long-term control of diabetes mellitus.
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Hemoglobin: The oxygen-carrying pigment and predominant protein in the red blood cells. Hemoglobin forms an unstable, reversible bond with oxygen. In its oxygenated state it is called oxyhemoglobin and is bright red. In the reduced state it is called deoxyhemoglobin and is purple-blue.
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Hemoglobin A: Normal adult hemoglobin, the main type of hemoglobin after infancy. The A stands for Adult.

Hemoglobin A1C: The main fraction of glycosylated hemoglobin (glycohemoglobin) which is hemoglobin to which glucose is bound. Hemoglobin A1C is tested to monitor the long-term control of diabetes mellitus.
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Hyperglycemia: A high blood sugar. An elevated level specifically of the sugar glucose in the blood.
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Hypoglycemia: Low blood sugar (glucose). When symptoms of hypoglycemia occur together with a documented blood glucose under 45 mg/dl, and the symptoms promptly resolve with the administration of glucose, the diagnosis of hypoglycemia can be made with some certainty. Hypoglycemia is only significant when it is associated with symptoms.
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Insulin: A natural hormone made by the pancreas that controls the level of the sugar glucose in the blood. Insulin permits cells to use glucose for energy. Cells cannot utilize glucose without insulin.
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Kidney: One of a pair of organs located in the right and left side of the abdomen which clear "poisons" from the blood, regulate acid concentration and maintain water balance in the body by excreting urine. The kidneys are part of the urinary tract. The urine then passes through connecting tubes called "ureters" into the bladder. The bladder stores the urine until it is released during urination.

Molecule: The smallest unit of a substance that can exist alone and retain the character of that substance.

Pigment: A substance that gives color to tissue. Pigments are responsible for the color of skin, eyes, and hair.

Protein: A large molecule composed of one or more chains of amino acids in a specific order determined by the base sequence of nucleotides in the DNA coding for the protein.
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Random: The process by which an outcome is determined solely by chance, for example, by a coin flip.
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Red blood cells: The blood cells that carry oxygen. Red cells contain hemoglobin and it is the hemoglobin which permits them to transport oxygen (and carbon dioxide). Hemoglobin, aside from being a transport molecule, is a pigment. It gives the cells their red color (and their name).
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Sickle cell disease: A genetic blood disorder caused by the presence of an abnormal form of hemoglobin. These hemoglobin molecules tend to aggregate after unloading oxygen forming long, rod-like strictures that force the red cells to assume a sickle shape. Unlike normal red cells, which are usually smooth and malleable, the sickle red cells cannot squeeze through small blood vessels. When the sickle cells block small blood vessels, the organs are deprived of blood and oxygen. This leads to periodic episodes of pain and damages the vital organs. Sickle red cells die after only about 10 to 20 days. Instead of the usual 120 days or so. Because they cannot be replaced fast enough, the blood is chronically short of red cells, causing anemia. The gene for sickle cell anemia must be inherited from both parents for the illness to occur in children. A child with only one copy of the gene may have sickle-cell traits but no symptoms of illness.
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Thalassemia: Not just one disease but rather a complex series of genetic (inherited) disorders all of which involve underproduction of hemoglobin, the indispensable molecule in red blood cells that carries oxygen. The globin part of hemoglobin is made up of 4 polypeptide chains (usually 2 chains of one type and 2 chains of another type of chain). In thalassemia, there is a mutation (change) in one of the types of globin chains. Depending upon which globin chain is affected, the mutation typically leads to underproduction (or absence) of that globin chain, a deficiency of hemoglobin, and anemia.

Therapy: The treatment of disease.
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Uremia: The presence of excessive amounts of urea in the blood, which may be a sign of kidney disease or failure.
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