A client is prescribed an intravenous heparin drip for treatment of a pulmonary embolism. Which laboratory test will the nurse monitor to help evaluate the therapeutic effects of the drug

A. Prothrombin time (PT): PT measures the extrinsic coagulation pathway and is primarily used to monitor warfarin therapy, not heparin. While it may be affected by some clotting disorders, it is not the best test to assess the therapeutic effect of heparin. B. Partial thromboplastin time (PTT): PTT evaluates the intrinsic and common coagulation pathways and is the primary test used to monitor the anticoagulant effects of intravenous heparin. Therapeutic PTT levels help ensure effective clot prevention while minimizing bleeding risk. C. International normalized ratio (INR): INR standardizes PT results and is used specifically for monitoring warfarin therapy. It does not provide useful data on heparin’s effects, making it inappropriate for evaluating heparin infusion efficacy. D. Platelet count: Monitoring platelet count is essential for detecting heparin-induced thrombocytopenia, a serious adverse effect. However, it does not reflect the therapeutic anticoagulation level and is not used to determine heparin dose adjustments.