College Answer

a)   What is the APTT mixing test and what is its significance in this patient?

It involves mixing patient’s plasma with normal pooled platelet free plasma. If it normalized then the elevated APTT is due to factor deficiency. Partial correction suggests an inhibitor.

These results suggest antiphospholipid syndrome in this patient

Discussion

Mixing studies and their intepretation are discussed elsewhere. Essentially, the failure of normal plasma to correct the coagulopathy suggests that all the factors which it had contributed to the patient's plasma were inhibited by some sort of mysterious inhibitory factor. In the absence of anticoagulant therapy, one would be forced to blame some sort of antiphospholipid antibody.