The client with atrial fibrillation is receiving warfarin (Coumadin). Which laboratory test should be monitored to determine the effectiveness of the therapy?
Correct Answer: A
Rationale: Monitoring Prothrombin time (PT) and international normalized ratio (INR) is crucial when a client is on warfarin therapy. These tests assess the clotting ability of the blood and help determine the appropriate dosage of warfarin to prevent complications such as bleeding or clotting events. PT and INR values within the therapeutic range indicate the effectiveness of warfarin in managing atrial fibrillation. Choice B, activated partial thromboplastin time (aPTT), is not typically used to monitor warfarin therapy; it is more commonly used to assess the effectiveness of heparin therapy. Choice C, complete blood count (CBC), does not directly assess the anticoagulant effect of warfarin. Choice D, fibrinogen level, is not a primary test for monitoring warfarin therapy; it is more relevant in assessing conditions like disseminated intravascular coagulation.