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The correct answer is B. PT 1½ to 2 times the control. In patients receiving warfarin therapy for conditions such as deep vein thrombophlebitis, monitoring the prothrombin time (PT) is essential to assess the effectiveness of the medication. The standard target PT range for patients on warfarin is typically 1½ to 2 times the control value. This range indicates that the patient's blood is clotting at a rate considered therapeutic to prevent the formation of additional blood clots.

Option A (PTT 1½ to 2 times the control) is not the preferred laboratory value for monitoring warfarin therapy. Although the partial thromboplastin time (PTT) is useful for monitoring heparin therapy, it is not typically used to monitor warfarin therapy.

Option C (INR of 3 to 4) is related to the PT value, but the PT value itself is more commonly used to monitor warfarin therapy directly.

Option D (Hematocrit of 32%) is not a laboratory value typically used to monitor warfarin therapy. Hematocrit is a measure of the percentage of red blood cells in the blood and is not directly linked to the monitoring of anticoagulation therapy with warfarin.