A Patient Who Is on an Anticoagulant (Coumadin) Asks, "What

A patient who is on an anticoagulant (Coumadin) asks, "What did the primary care provider mean when he said I was to have my blood tested every 2 weeks?" The nurse explains, "It is important to monitor the effects of the drug to see how long it takes your blood to clot. The blood test the primary care provider was talking about is the:

A) complete blood count (CBC) ."
B) activated partial thromboplastin time (APTT) ."
C) international normalized ratio (INR) ."
D) erythrocyte sedimentation rate (ESR) ."