A suspected bleeding disorder patient shows prolonged aPTT that does not correct with 1:1 mixing with normal plasma. Which condition is most likely?

• A. platelet function defect
• B. presence of a factor inhibitor
• C. von Willebrand disease
• D. factor deficiency easily corrected

Answer: (B)

Prolonged aPTT that does not correct with a 1:1 mixing study points to an inhibitor rather than a simple factor deficiency. When normal plasma is added to a sample with a factor deficiency, the missing factor from the normal plasma corrects the clotting time, so the aPTT tends toward normal. But if an inhibitor is present—such as an anti-factor VIII inhibitor or a lupus anticoagulant—the inhibitor blocks the coagulation factor activity regardless of how much normal plasma is added, so the aPTT remains prolonged. This pattern distinguishes an inhibitor from a straightforward deficiency. Platelet function defects or von Willebrand disease can affect bleeding but don’t produce a persistent lack of correction in the mixing test in the same way, and a clearly deficient factor that easily corrects would behave like a true deficiency, not an inhibitor. Hence, the most likely scenario is the presence of a factor inhibitor.