Antithrombin (AT) is a single-stranded glycoprotein synthesised in the liver with a plasma concentration of approximately 150 μg/mL and a molecular weight of approximately 59,000 Da1. It is a complex molecule with multiple biologically important properties. It is a serine protease inhibitor (serpin) that inactivates many enzymes in the coagulation cascade2,3. Indeed, it is the key inhibitor of the coagulation system and is estimated to provide 80% of the inhibitory activity against thrombin but it also inhibits activated factors X, IX, VII, XI, and XII. AT has a great affinity for thrombin and is also known as heparin cofactor as it is responsible for the anticoagulant effect of heparin. Heparins markedly accelerate the rate of complex formation between AT and the serine proteases thus increasing AT inhibitory activity 5,000–40,000-fold4. AT also has remarkable anti-inflammatory properties, several of which result from its actions in the coagulation cascade. Other anti-inflammatory properties of AT involve direct interactions with endothelial cells, leading to the release of prostacyclin, which also mediates its anti-platelet effect3. In addition, recent evidence of interactions of the endothelial cell growth factors bFGF (basic fibroblast growth factor) and VEGF (vascular endothelial cell growth factor) with a heparin-like molecule in matrix provide the rationale for further investigation into the possible role of AT as a potent anti-angiogenic factor5. Normal values of AT activity in the plasma range from 80% to 120%. In normal conditions, its biological half-life is 1.5–2.5 days. In conditions of acquired deficiency and in the presence of heparin, the half-life of AT can be notably shorter, being reduced to only a few hours6.