A blood clot or thrombus can form in the vessel walls of arteries or veins. An arterial thrombus is a very dangerous clot that can obstruct the flow of blood to major organs and cause complications such as stroke, transient ischemic attack (TIA or mini-stroke), heart attack, or peripheral arterial disease.

A venous thrombus can occur in the deep veins of the body such as a deep leg vein (deep vein thrombosis, DVT) or a blood vessel of the lung. In DVT, a piece of the clot may detach and travel to the lungs where it can lodge and create another blockage. This is a potentially life-threatening complication of deep vein thrombosis called pulmonary embolism (PE). DVT and PE are collectively termed venous thromboembolism (VTE).

The treatments that are available for treating VTE include anticoagulant medications such as heparin or warfarin. These are also called blood thinners. These drugs do not break a clot down but reduce the clot’s ability to coagulate and prevent further growth of the clot. This can also reduce the risk of a clot fragment breaking off and travelling to the lung or brain. Anti-coagulants also help prevent the recurrence of clots.

In summary, the aims of blood thinning treatments in thrombosis include:

• Preventing the clot from growing bigger
• Preventing the formation of new clots
• Preventing the clot from breaking off and moving to major body organs
• Preventing recurrence
• Preventing long-term complications

Medications

Heparin
Heparin is given by injection or drip into a vein as unfractionated heparin. The blood coagulability needs to be closely monitored while using heparin because blood that has become too thin can lead to uncontrolled bleeding. A calculation called the International Normalized Ratio (INR) is used to standardize the results of prothrombin time and monitor the therapy. Without warfarin, a person with DVT may have an INR of around 1.0 (typically 0.8 to 1.2) and the goal of treatment is usually to achieve an INR of around 2.0 to 3.0.