After Confirmation of a Deep Vein Thrombosis (DVT)and Pulmonary Embolus

After confirmation of a deep vein thrombosis (DVT) and pulmonary embolus in a patient,a baseline coagulation screen and platelet count are obtained.His fibrinogen is 620 mg/dL.When the PTT is performed at 6 hours after initiation of therapy,it is 45 seconds (reference range,25 to 37 seconds) .What should be done?

A) Report the PTT as not responding.
B) Monitor the patient with the chromogenic anti-Xa assay.
C) Add an additional standard amount of heparin to the patient plasma to improve the sensitivity.
D) Add a standard amount of antithrombin to the patient plasma to improve the sensitivity.