A mixing study was performed and there was no correction of either the prolonged PT or the aPTT. What would be the likely coagulation abnormality to consider?

• A. Lupus inhibitor
• B. Factor XIII deficiency
• C. Hemophilia A
• D. Factor V Leiden

Answer: (A)

In a mixing study, failure of the prolonged times to correct after mixing patient plasma with normal plasma points to an inhibitor rather than a true factor deficiency. Lupus anticoagulant is a classic antiphospholipid antibody that interferes with phospholipid-dependent coagulation steps, so it prolongs tests like the aPTT (and sometimes the PT) and does not correct when normal plasma is added. That’s why lupus anticoagulant is the most likely abnormality to consider when there’s no correction of either prolonged PT or aPTT.

Factor deficiencies, such as factor VIII deficiency causing hemophilia A, would usually correct with mixing because the normal plasma supplies the missing factor. Factor XIII deficiency affects clot stabilization more than the initial PT/aPTT times and is not typically detected by these standard tests. Factor V Leiden is a genetic resistance to activated protein C and isn’t diagnosed by a mixing study, so it doesn’t fit the pattern described.