How can the use of anticoagulants such as warfarin affect phlebotomy practice or results?

• A. Warfarin increases bleeding risk; ensure adequate hemostasis and monitor PT/INR results separately; phlebotomy technique remains the same, but sample handling may affect coagulation results
• B. Warfarin reduces bleeding risk so no pressure is needed
• C. Warfarin makes samples always positive for clotting tests
• D. Warfarin requires drawing from a different vein

Answer: (C)

Anticoagulants like warfarin affect how easily blood clots. Warfarin inhibits vitamin K–dependent clotting factors, so it raises the risk of bleeding and prolongs coagulation tests such as PT/INR. In phlebotomy practice, this means you must be extra careful to achieve hemostasis after drawing blood (apply firm pressure, monitor the puncture site, and watch for bruising). When testing, PT/INR results may be prolonged and need to be interpreted in the clinical context, so you handle and label samples correctly and ensure proper collection for coagulation studies (for example, using the correct citrate-containing tube and gentle inversion). The actual puncture technique remains the same, but your approach to post-draw pressure and to interpreting coagulation results changes. It is not necessary to draw from a different vein, and warfarin does not make samples “always positive for clotting”; it typically causes longer clotting times, not true clotting.