Prolonged bleeding is the expected complication for a patient on warfarin therapy. Warfarin is an anticoagulant, meaning it interferes with normal clot formation and can increase bleeding time after venipuncture. The phlebotomist should be alert for delayed hemostasis, apply firm pressure after needle removal, avoid having the patient bend the arm sharply, and confirm that bleeding has stopped before applying a bandage and leaving the patient. Blood clotting is the opposite of the expected medication effect. Hemostasis is the normal stopping of bleeding, not a complication. Petechiae can occur from tourniquet pressure, fragile capillaries, or platelet-related issues, but in this question the medication-specific risk is prolonged bleeding. Proper technique reduces complications: release the tourniquet, withdraw the needle smoothly, activate the safety device, apply pressure, and monitor the puncture site. Reference topics: Routine Blood Collections; post-procedure care; anticoagulant therapy; bleeding complications; hemostasis; patient observation. NHA includes routine venipuncture complications and post-collection care within the CPT test plan.

==========