Which lab value is monitored to assess anticoagulation intensity in heparin therapy?

• A. PTT
• B. INR
• C. Platelet count
• D. Hemoglobin

Answer: (A)

Monitoring unfractionated heparin therapy relies on the activated partial thromboplastin time, aPTT. This test measures how long blood plasma takes to clot via the intrinsic and common pathways. Heparin works by boosting antithrombin III, which inhibits thrombin and factor Xa, so higher heparin activity makes clots take longer to form. Clinically, we adjust heparin dosing to keep the aPTT within a therapeutic range—usually about 1.5 to 2.5 times the patient’s baseline value, though exact targets depend on the protocol.

Other common labs don’t measure anticoagulation intensity: INR reflects the extrinsic pathway and is used to monitor warfarin; platelet count tracks platelet quantity and risk of heparin-induced thrombocytopenia, not the degree of anticoagulation; hemoglobin indicates red blood cell mass and bleeding status, not anticoagulation level.