Low-molecular-weight heparin primarily inhibits which clotting factor?

Low-molecular-weight heparin primarily inhibits which clotting factor?

• A. Factor IIa (thrombin)
• B. Factor Xa
• C. Factor VIIa
• D. Factor IXa

Answer: (B)

Low-molecular-weight heparin works by binding antithrombin III and greatly enhancing its inhibition of Factor Xa. Its shorter chain length makes it less able to bridge antithrombin III to thrombin (Factor IIa), so anti-IIa activity is reduced compared with anti-Xa activity. This results in a predominant inhibition of Factor Xa, which stops the conversion of prothrombin to thrombin and thereby limits fibrin formation. The other factors listed are not the primary targets of LMWH.

Low-molecular-weight heparin works by binding antithrombin III and greatly enhancing its inhibition of Factor Xa. Its shorter chain length makes it less able to bridge antithrombin III to thrombin (Factor IIa), so anti-IIa activity is reduced compared with anti-Xa activity. This results in a predominant inhibition of Factor Xa, which stops the conversion of prothrombin to thrombin and thereby limits fibrin formation. The other factors listed are not the primary targets of LMWH.