During heparin therapy for a pulmonary embolism, which blood test should be monitored closely?

During heparin therapy for a pulmonary embolism, which blood test should be monitored closely?

• A. International normalized ratio (INR)
• B. Partial thromboplastin time (PTT)
• C. Platelet function assay (PFA)
• D. Prothrombin time (PT)

Answer: (B)

Heparin’s effect is best tracked with a test that reflects the intrinsic pathway of coagulation. The PTT (activated partial thromboplastin time) measures how long it takes plasma to clot via the intrinsic and common pathways, and heparin prolongs this time in a dose-dependent way by boosting antithrombin III to inhibit thrombin and factor Xa. By monitoring the PTT and adjusting the heparin dose to a therapeutic range, clinicians balance preventing clot growth with minimizing bleeding risk. INR and PT assess the extrinsic pathway and are mainly used to monitor warfarin therapy, not heparin. Platelet function tests aren’t used to gauge heparin effect, and routine monitoring of low-molecular-weight heparin isn’t required (though anti-Xa levels can be used in special populations).

Heparin’s effect is best tracked with a test that reflects the intrinsic pathway of coagulation. The PTT (activated partial thromboplastin time) measures how long it takes plasma to clot via the intrinsic and common pathways, and heparin prolongs this time in a dose-dependent way by boosting antithrombin III to inhibit thrombin and factor Xa. By monitoring the PTT and adjusting the heparin dose to a therapeutic range, clinicians balance preventing clot growth with minimizing bleeding risk. INR and PT assess the extrinsic pathway and are mainly used to monitor warfarin therapy, not heparin. Platelet function tests aren’t used to gauge heparin effect, and routine monitoring of low-molecular-weight heparin isn’t required (though anti-Xa levels can be used in special populations).