Low-molecular-weight heparin is best monitored by which laboratory test?

Low-molecular-weight heparin is best monitored by which laboratory test?

• A. Activated partial thromboplastin time
• B. Prothrombin time
• C. Anti-Xa assay
• D. Thrombin time

Answer: (C)

Low-molecular-weight heparin acts mainly by inhibiting factor Xa through its interaction with antithrombin. Because of this selective action, the test that best reflects its anticoagulant effect is the anti-Xa assay, which directly measures how much factor Xa is inhibited in the patient’s plasma. Activated partial thromboplastin time is designed to reflect the activity of unfractionated heparin and often does not reliably correlate with LMWH activity, since LMWH causes only small or inconsistent prolongation of APTT at therapeutic or prophylactic doses. Prothrombin time evaluates the extrinsic pathway and is not significantly affected by LMWH. Thrombin time is highly sensitive to heparin in general, but LMWH’s effect on TT is variable and not used for routine monitoring. So, anti-Xa assay is the best choice to monitor LMWH therapy.

Low-molecular-weight heparin acts mainly by inhibiting factor Xa through its interaction with antithrombin. Because of this selective action, the test that best reflects its anticoagulant effect is the anti-Xa assay, which directly measures how much factor Xa is inhibited in the patient’s plasma.

Activated partial thromboplastin time is designed to reflect the activity of unfractionated heparin and often does not reliably correlate with LMWH activity, since LMWH causes only small or inconsistent prolongation of APTT at therapeutic or prophylactic doses. Prothrombin time evaluates the extrinsic pathway and is not significantly affected by LMWH. Thrombin time is highly sensitive to heparin in general, but LMWH’s effect on TT is variable and not used for routine monitoring.

So, anti-Xa assay is the best choice to monitor LMWH therapy.