A client diagnosed with a PE is placed on a heparin drip. The nurse knows that she must monitor which of the following?

A. WBC: The white blood cell count helps identify infection or inflammation but is not used to monitor the therapeutic effect of heparin. It does not provide information on anticoagulation status or bleeding risk. B. D-dimer: D-dimer is useful for diagnosing or ruling out a PE initially but is not used to monitor treatment. Once anticoagulation has begun, D-dimer levels are not reliable indicators of therapeutic effectiveness. C. PT/INR: PT/INR is used to monitor warfarin therapy, not heparin. Heparin affects the intrinsic pathway of the coagulation cascade, and PT/INR does not accurately reflect its anticoagulant effect. D. aPTT: The activated partial thromboplastin time (aPTT) is the correct test to monitor heparin therapy. It measures the efficacy of the intrinsic clotting pathway and helps determine if the heparin dose is within the therapeutic range.