A patient with post - paum hemorrhage had about 2 liters of blood loss. Investigation revealed normal PT and a prolonged aPTT. Test to differentiate between coagulation factor deficiency and factor inhibitor is:

Mixing studies are used to distinguish between a factor deficiency and an inhibitor. Normal plasma and patient plasma are mixed in a 1:1 ratio, and the aPTT or PT is determined immediately and after incubation at 37degC for 30, 60, and/or 120 min. Isolated factor deficiencies aPTT will correct with mixing and stay corrected with incubation Lupus anticoagulant mixing and incubation will show no correction Acquired neutralizing factor antibodies initial assay may or may not correct immediately after mixing but will prolong with incubation at 37degC. Other inhibitors or interfering substances- heparin, fibrin split products, and paraproteins