Practice Question
A nurse is caring for a client who has a new prescription for warfarin. The nurse should use the results of which of the following diagnostic tests to monitor the effect of this therapy?
Answer Choices:
Correct Answer:
PT/INR (Prothrombin time & International Normalized Ratio)
Rationale:
🧪 Warfarin works by inhibiting vitamin K–dependent clotting factors in the extrinsic pathway, which is best assessed with PT and INR.
🧪 The INR standardizes PT values, allowing safe dose adjustments across different labs and settings.
🧪 For most indications such as DVT or atrial fibrillation, the therapeutic INR range is usually 2.0–3.0, balancing clot prevention and bleeding risk.
🧪 Regular PT/INR monitoring guides the provider in increasing, decreasing, or maintaining the warfarin dose.
🧪 Because it directly reflects warfarin’s anticoagulant effect, PT/INR is the primary and correct test to monitor this therapy.
White blood cell count (WBC)
🧪 The WBC is used to assess infection, inflammation, or immune response, not clotting or anticoagulant effect.
🧪 Warfarin does not primarily affect white blood cell production, so changes in WBC do not show whether the dose is therapeutic.
🧪 A normal WBC could falsely reassure the nurse or client that everything is “fine” with the medication when coagulation status is unknown.
🧪 WBC monitoring may still be useful for overall health, but it is not specific to warfarin safety or effectiveness.
🧪 Therefore, relying on WBC to monitor warfarin would be inappropriate and unsafe.
Activated partial thromboplastin time (aPTT)
🧪 The aPTT measures the intrinsic pathway of coagulation, and is the standard test used to monitor heparin therapy, not warfarin.
🧪 Warfarin affects the extrinsic pathway, so the PT/INR, not aPTT, reflects its anticoagulant effect.
🧪 If the nurse uses aPTT for warfarin monitoring, important INR changes could be missed, putting the client at risk for thrombosis or bleeding.
🧪 This confusion could lead to inappropriate dose adjustments, making therapy unsafe.
🧪 Thus, aPTT is not the correct test for monitoring warfarin.
Platelet count
🧪 A platelet count measures the number of platelets involved in primary hemostasis, but warfarin does not usually cause thrombocytopenia.
🧪 Platelet counts are more critical for drugs that lower platelets or conditions like heparin-induced thrombocytopenia.
🧪 While platelets are relevant in overall bleeding risk, they do not indicate how strongly warfarin is anticoagulating the blood.
🧪 A normal platelet count can coexist with a dangerously elevated INR, so relying on platelets alone is unsafe.
🧪 Therefore, platelet count is supportive information, but not the primary monitoring tool for warfarin therapy.
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This question is from ☑️Custom NSGP 132 Fall 25 Exam 2 which contains 39 questions.
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Question Details
- Category: RN Nursing Exam(s)
- Subcategory: ATI Exam(s)
- Domain: RN ATI MedSurg
- Answer Choices: 4