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…
hemophilia An inherited disorder in which the ability of blood to clot normally is impaired. There are two types of hemophilia: hemophilia A and hemophilia B.
hemophilia A Classic hemophilia, which is due to a profound deficiency in the activity of clotting factor VIII. Affected individuals suffer hemorrhage into joints and muscles, easy bruising, and prolonged bleeding from wounds. The disease is inherited as an X-linked trait, so males are affected and females carry the gene. Treatment involves administration of blood…
hemophilia B Hemophilia due to deficiency of coagulation factor IX in the blood, which results in prolonged oozing after minor and major injuries, tooth extractions, or surgery. There is renewed bleeding after the initial bleeding has stopped. The gene for hemophilia B is on the X chromosome, so males are affected and females carry the…
hemoptysis Spitting up blood or blood-tinged sputum from the respiratory tract. Hemoptysis occurs when tiny blood vessels that line the lung airways are broken. Hemoptysis can be harmless such as from irritated bronchial tubes with bronchitis, or be serious such as from cancer of the lung.
hemorrhage Abnormal bleeding. A hemorrhage can be internal, and therefore invisible, or external, and therefore visible on the body. For example, bleeding into the spleen or liver is internal hemorrhage, and bleeding from a cut on the face is an external hemorrhage. See also bleeding.
hemorrhagic fever, epidemic See hemorrhagic fever, viral.
hemarthrosis Blood in a joint.
hematemesis Bloody vomit.
hematocrit The proportion of the blood that consists of red blood cells. Abbreviated Hct. Hct is expressed as a percentage. For example, an Hct of 25 percent means that there are 25 milliliters of red blood cells in 100 milliliters of blood. The normal ranges for Hct depend on the age and, after adolescence, the…
hematologist A physician who specializes in diagnosing and treating diseases of the blood.
hematology The branch of medicine concerned with the blood and blood-forming tissues, encompassing the diagnosis and treatment of disorders of the coagulation process, blood-cell formation, hemoglobin synthesis, and immune system, as well as cancers of blood and blood-forming organs such as leukemias and lymphomas.