Which laboratory value is used to monitor unfractionated heparin therapy?

Which laboratory value is used to monitor unfractionated heparin therapy?

• A. INR
• B. Platelet count
• C. aPTT
• D. Hematocrit

Answer: (C)

Unfractionated heparin affects the intrinsic pathway of coagulation, so its effect is best tracked by a test that measures how long the blood takes to clot when the intrinsic pathway is activated. That test is the activated partial thromboplastin time, or aPTT. As the heparin dose increases, the aPTT lengthens, and clinicians aim for a therapeutic range roughly 1.5 to 2.5 times the patient’s baseline or control value. Checking the aPTT several hours after starting therapy or after dose changes ensures the level is within the target window before adjusting the dose again. The other labs don’t monitor this effect: the INR reflects the extrinsic pathway and is used with warfarin therapy; platelet count helps assess risk of heparin-induced thrombocytopenia and bleeding but doesn’t measure anticoagulant activity; hematocrit indicates red cell volume and potential bleeding or dehydration but not anticoagulation. If a patient is on low molecular weight heparin, an anti-Xa level—not aPTT—is typically used to monitor therapy.

Unfractionated heparin affects the intrinsic pathway of coagulation, so its effect is best tracked by a test that measures how long the blood takes to clot when the intrinsic pathway is activated. That test is the activated partial thromboplastin time, or aPTT. As the heparin dose increases, the aPTT lengthens, and clinicians aim for a therapeutic range roughly 1.5 to 2.5 times the patient’s baseline or control value. Checking the aPTT several hours after starting therapy or after dose changes ensures the level is within the target window before adjusting the dose again.

The other labs don’t monitor this effect: the INR reflects the extrinsic pathway and is used with warfarin therapy; platelet count helps assess risk of heparin-induced thrombocytopenia and bleeding but doesn’t measure anticoagulant activity; hematocrit indicates red cell volume and potential bleeding or dehydration but not anticoagulation. If a patient is on low molecular weight heparin, an anti-Xa level—not aPTT—is typically used to monitor therapy.