Dictionary

hemoglobin A Normal adult hemoglobin, the main type of hemoglobin found after infancy. The A stands for adult.

hemoglobin A1c A minor component of hemoglobin to which glucose is bound. Abbreviated HbA1c. HbA1c levels depend on the blood glucose concentration: The higher the glucose concentration in blood, the higher the level of HbA1c. Levels of HbA1c are not influenced by daily fluctuations in the blood glucose concentration but reflect the average glucose levels…

hemoglobin E Normal embryonic hemoglobin, the main type of hemoglobin found in the human embryo. The E stands for embryonic and also for epsilon, a chain that is unique to embryonic hemoglobin. Originally known as Gower-2.

hemoglobin F Normal fetal hemoglobin, the main type of hemoglobin found in the fetus and newborn baby. The F stands for fetal.

hemoglobin S The most common type of abnormal hemoglobin, which is found in people with sickle cell trait and sickle cell anemia. It differs from hemoglobin A only by a single amino acid substitution. The S stands for sickle. See also anemia, sickle cell; sickle cell trait.

hemoglobinuria The presence of free hemoglobin in the urine, which may make the urine look dark. Normally, there is no hemoglobin in the urine. Hemoglobinuria is a sign of a number of abnormal conditions, such as bleeding and paroxysmal nocturnal hemoglobinuria.

hemolysis Breakage of red blood cells. This occurs to a minor degree normally as red blood cells age. However, excessive hemolysis is very abnormal and leads to hemolytic anemia. See also hemolytic anemia.

hemolytic anemia Anemia due to the destruction, rather than underproduction, of red blood cells. Hemolytic anemia can result from a medication reaction, from the immune system attacking the red blood cells (autoimmune hemolytic anemia), from destruction of blood cells passing through diseased heart valves, and other causes.

hemolytic disease of the newborn Abnormal breakup of red blood cells in a fetus or newborn. Hemolytic disease of the newborn is usually due to antibodies made by the mother that are directed against the baby’s red blood cells. It is typically caused by Rh incompatibility (a difference between the Rh blood groups of mother…

hemolytic jaundice, congenital See spherocytosis, hereditary.

hemolytic-uremic syndrome A condition involving the breakup of red blood cells (hemolysis) and kidney failure. Abbreviated HUS. HUS is the most common cause of acute kidney failure in infants and young children, but the condition can also occur in adults. The disease results in damage to the lining of blood vessels in the kidney, leading…

hemophagocytic lymphohistiocytosis A rare, cancer-like disorder resulting from an impaired immune system in which macrophages and lymphocytes grow abnormally and accumulate in the body’s organs, including the liver, spleen, bone marrow, central nervous system, and skin. Hemophagocytic lymphohistiocytosis can be an inherited condition, or it can occur as a result of immunosuppression (as in organ…