A client is on warfarin therapy. Which laboratory value indicates a need to increase the dosage?

• A. aPTT 38 seconds
• B. INR 1.1
• C. PT 22 seconds
• D. D-dimer negative

Answer: (B)

Monitoring warfarin relies on the INR, which standardizes the prothrombin time across labs to gauge how anticoagulated the patient is. The goal is to keep the INR in the therapeutic range (typically around 2.0–3.0 for many indications). An INR of 1.1 is below that range, meaning the blood is not anticoagulated enough and the dose of warfarin should be increased to reach therapeutic protection.

Understanding the other values helps: aPTT measures the intrinsic pathway and is used mainly to monitor heparin therapy, not warfarin. A plain PT value like 22 seconds can be prolonged, but PT results vary by lab; INR standardizes this, making it the reliable measure for warfarin management. D-dimer reflects fibrin degradation and active clot breakdown, not the level of anticoagulation with warfarin.