This patient is most likely suffering from an immediate-acting coagulation inhibitor; most commonly, lupus anticoagulant. Notice that the addition of normal pooled plasma does not correct upon initial or incubated mix, which means that the inhibitor is not time or temperature-dependent.

Factor VIII is not the correct answer as a factor deficiency would have corrected upon the addition of normal pooled plasma. Factor VII is not the correct answer, as the aPTT assay does not account for factor VII activity or concentration.

The laboratorian completed the mixing study ordered for John Doe. The results are as follows:

Initial aPTT result: 167 seconds

Initial 1:1 Mix with Normal Pooled Plasma: 158 seconds

Incubated 1:1 Mix with Normal Pooled Plasma: 150 seconds

Which of the choices below would most likely explain the results for this patient?