An aPTT performed on a patient on high-dose warfarin therapy would be expected to be:

An aPTT performed on a patient on high-dose warfarin therapy would be expected to be:

• A. Decreased
• B. Increased
• C. Unchanged
• D. Variable

Answer: (B)

Warfarin reduces vitamin K–dependent clotting factors II, IX, and X, which slows the clotting process. The aPTT measures the intrinsic and common pathways, so when these factors are depleted, the time to form a clot increases. With high-dose warfarin, this depletion is substantial, leading to a prolonged aPTT. While PT/INR is the primary test for monitoring warfarin, the aPTT can also be prolonged at high doses. Thus, the expected result is an increased aPTT. Decreased or unchanged would be unlikely at high dose, and while aPTT can vary in some situations, the typical response with high-dose warfarin is prolongation.

Warfarin reduces vitamin K–dependent clotting factors II, IX, and X, which slows the clotting process. The aPTT measures the intrinsic and common pathways, so when these factors are depleted, the time to form a clot increases. With high-dose warfarin, this depletion is substantial, leading to a prolonged aPTT. While PT/INR is the primary test for monitoring warfarin, the aPTT can also be prolonged at high doses. Thus, the expected result is an increased aPTT. Decreased or unchanged would be unlikely at high dose, and while aPTT can vary in some situations, the typical response with high-dose warfarin is prolongation.