An abnormal APTT caused by a pathological circulating anticoagulant is:

An abnormal activated partial thromboplastin time (APTT) that is caused by a pathological circulating anticoagulant, such as an inhibitor, will not be corrected with normal plasma. This is due to the nature of circulating anticoagulants, which interfere with the coagulation process by inactivating specific clotting factors.

In cases where the APTT is prolonged due to such an inhibitor, adding normal plasma does not restore normal function because the inhibitor will continue to inactivate the factors present in the normal plasma. Therefore, even though normal plasma contains all the necessary clotting factors, the presence of the inhibitor prevents effective coagulation, which results in the APTT remaining prolonged.

In contrast, if the APTT were prolonged due to a deficiency of factor VIII or IX, it could be corrected by the addition of factor-deficient plasma, as the underlying issue would be the lack of those specific factors rather than the presence of an inhibitor. This highlights the distinction between simple factor deficiencies and the more complex scenario involving circulating anticoagulants or inhibitors.