In mixing studies for a prolonged aPTT, what would correction suggest?

• A. Prolonged aPTT corrects with 1:1 mixing, indicating factor deficiency.
• B. Prolonged aPTT does not correct, indicating inhibitor.
• C. PT prolonged, not aPTT
• D. Bleeding time prolongation

Answer: (A)

Mixing studies with a prolonged aPTT are used to tell whether the issue is a deficiency of intrinsic pathway factors or the presence of an inhibitor. If the prolonged aPTT corrects when patient plasma is mixed 1:1 with normal plasma, the normal plasma supplies the missing factor(s) and the clotting time shortens toward normal. That pattern points to a quantitative factor deficiency (such as factor VIII, IX, or XI deficiency).

If there is no correction with mixing, an inhibitor is suspected—these inhibitors (like a lupus anticoagulant or a factor-specific inhibitor) interfere with the clotting process even in the presence of normal plasma, so the prolonged time persists.

The other options aren’t about the intrinsic pathway mixing result: a prolonged PT would reflect the extrinsic pathway and isn’t assessed by the aPTT mixing test, and bleeding time is unrelated to the activation of the coagulation cascade evaluated by aPTT.