A nurse is caring for a client who had a myocardial infarction and is receiving unfractionated heparin. Which of the following laboratory tests should the nurse monitor to assess the effectiveness of the medication?

Rationale: A. High-density lipoprotein (HDL) is a lipid panel value used to assess cardiovascular risk over time, not to monitor anticoagulation therapy. It does not reflect the therapeutic effectiveness of heparin. B. Hemoglobin A1c reflects long-term blood glucose control over approximately 2–3 months and is used in the management of diabetes mellitus. It has no role in monitoring heparin therapy. C. Activated partial thromboplastin time (aPTT) is the primary laboratory test used to monitor the effectiveness of unfractionated heparin therapy. Heparin prolongs the intrinsic and common coagulation pathways, and the aPTT is used to ensure the client remains within the therapeutic range, typically 1.5 to 2.5 times the normal value, to prevent clot formation while minimizing bleeding risk. D. Prothrombin time (PT) is used to monitor warfarin therapy, not heparin. PT assesses the extrinsic pathway of coagulation and is not the appropriate test for evaluating unfractionated heparin effectiveness.