What is the purpose of unfractionated heparin?

• A. To dissolve clots.
• B. To decrease the body's production of clotting factors.
• C. To accelerate clot formation.
• D. To slow the time it takes the blood to clot thereby keeping the current clot from getting bigger and preventing new ones from forming.

Answer: (D)

Unfractionated heparin works as an anticoagulant by boosting the activity of antithrombin III, which in turn inhibits thrombin (factor IIa) and factor Xa. This reduces the generation of fibrin and slows the propagation of clots, preventing a clot from getting bigger and stopping new clots from forming. It does not dissolve clots—that would be the job of a thrombolytic agent. It also doesn’t reduce the body’s production of clotting factors; it acts on existing coagulation factors to prevent their effects. Clinically, this is why heparin is used to prevent and treat clot formation, with monitoring (like aPTT) to keep treatment in the therapeutic range.