H

Hageman Factor

See Factor XII deficiency

Haplotype

Closely linked genetic markers that are inherited together.

Heart

The chambered muscular organ in vertebrates that pumps blood received from the veins into the arteries, thereby maintaining the flow of blood through the entire circulatory system. Gray's Anatomy

Heart Attack

Sudden interruption or insufficiency of the supply of blood to the heart, typically resulting from occlusion or obstruction of a coronary artery and often characterized by severe chest pain.

Hematology

The branch of biology which deals with blood.

Hemocrit (HCT)

The percent of whole blood that is comprised of red blood cells. The hematocrit is a compound measure of RBC number and size. MEDLINEplus

Hemocyte

A blood cell, especially of an invertebrate animal.

Hemoglobin

Hgb; Hb. The protein which carries oxygen in the blood, and it is contained in red blood cells. Abnormalities of the hemoglobin value indicate defects in red blood cell homeostasis (balance). Both low and high values can indicate disease states. MEDLINEplus

Hemophilia

A group of inherited blood coagulation disorders characterized by decreased or dysfunctional clotting factors.

Hemophilia A

See Factor VIII deficiency hemophilia.

Hemophilia B

See Factor IX hemophilia.

Hemorrhage

Excessive discharge of blood from the blood vessels; profuse bleeding.

Hemostasis

The delicate balance between bleeding and excessive coagulation.

Heparin

An anticoagulant stored in, and released from the mast cells lying beneath the vascular endothelium.

Commercial heparins are extracted from animal tissues, purified, concentrated and have molecular weights of 3,000 to 57,000. Glycosaminoglycan and anticoagulant used to decrease the clotting ability of the blood and help prevent harmful clots from forming in the blood vessels. This medicine is sometimes referred to a blood thinner, although it does not actually thin the blood. Heparin interacts with antithrombin and other activated serine proteases resulting in anticoagulant activity. Heparin will not dissolve blood clots that have already formed, but it may prevent the clots from becoming larger and causing more serious problems.

Heparin is often used as a treatment for certain blood vessel, heart, and lung conditions. Heparin is also used to prevent blood clotting during open-heart surgery, bypass surgery, and dialysis. It is also used in low doses to prevent the formation of blood clots in certain patients, especially those who must have certain types of surgery or who must remain in bed for a long time. MEDLINEplus

Heparin Cofactor II

A thrombin inhibitor that demonstrates activation in the presence of heparin in a manner similar to antithrombin.

Heparin-associated thrombocytopenia (HAT)

Heparin-induced thrombocytopenia. HAT may present as a non-immune, self-limiting form of thrombocytopenia or an immune-based antibody - mediated, more severe form, and may be associated with thrombosis.

Hereditary

Inherited. Passed down through families.

Hirudin

A substance secreted by the buccal glands of leeches, capable of preventing coagulation by inactivating thrombin and used in medicine as an anticoagulant.

High-density Lipoprotein (HDL)

A complex of lipids and proteins in approximately equal amounts that functions as a transporter of cholesterol in the blood. High levels are associated with a decreased risk of atherosclerosis and coronary heart disease.

HIT

Heparin induced thrombocytopenia.

Homocysteine

A thiol containing amino acid that is produced by demethlyation of methionine. Hyperhomocysteinemia is a risk factor for both arterial and venous thrombosis.

HMW

High Molecular Weight.

HMW Kininogen

Fizgerald Factor

HRP

Horseradish Peroxidase.

Hyperlipidemia

Hyperlipemia. An excess of fats or lipids in the blood.

Hypofibrinogenemia

A low or deficient level of fibrinogen in the blood.

Hypoprothrombinemia

See Factor II deficiency