Heparin

Heparin is a naturally occurring anticoagulant produced by basophils and mast cells. It is used medically as an injectable anticoagulant and has the highest negative charge density of any known biological molecule. Heparin is used to prevent and treat deep vein thrombosis, pulmonary embolism, and arterial thromboembolism. It is also used in the treatment of myocardial infarction and during cardiopulmonary bypass and hemofiltration.

History

Heparin was discovered in 1916 by Jay McLean and William Henry Howell at Johns Hopkins University. The name "heparin" is derived from the Greek word for liver, "hepar," as it was first isolated from liver cells.

Mechanism of Action

Heparin works by activating antithrombin III, which in turn inhibits thrombin and factor Xa, key components in the coagulation cascade. This prevents the formation of fibrin clots and allows the body's natural clot lysis mechanisms to work unopposed.

Clinical Use

Heparin is administered intravenously or subcutaneously. It is commonly used in the following clinical scenarios:

• Deep vein thrombosis (DVT)
• Pulmonary embolism (PE)
• Acute coronary syndrome (ACS)
• Atrial fibrillation (AF) with embolization
• Cardiopulmonary bypass during open-heart surgery
• Hemodialysis

Side Effects

Common side effects of heparin include:

• Bleeding
• Thrombocytopenia
• Osteoporosis (with long-term use)
• Hypersensitivity reactions

Monitoring

The effectiveness of heparin is monitored using the activated partial thromboplastin time (aPTT) test. The target aPTT range is typically 1.5 to 2.5 times the normal value.

Heparin-Induced Thrombocytopenia (HIT)

One of the most serious complications of heparin therapy is heparin-induced thrombocytopenia (HIT). HIT is an immune-mediated adverse reaction that paradoxically increases the risk of thrombosis. It is diagnosed by a significant drop in platelet count and confirmed by laboratory tests for heparin-PF4 antibodies.

Low Molecular Weight Heparin (LMWH)

Low molecular weight heparins (LMWHs) are derived from standard heparin and have a more predictable anticoagulant response. They are used in similar clinical settings but have the advantage of not requiring regular aPTT monitoring.

See Also

• Anticoagulant
• Thrombosis
• Coagulation
• Warfarin
• Enoxaparin