Which of the following results is characteristic of lupus anticoagulant in mixing studies?

In the context of lupus anticoagulant and its effects on coagulation studies, the characteristic result during mixing studies is the behavior of the activated partial thromboplastin time (APTT) after mixing with normal plasma. In cases where lupus anticoagulant is present, the APTT will typically remain prolonged even after mixing with normal plasma and after incubation, indicating that a factor inhibition is taking place rather than a deficiency.

The normal APTT after mixing is not consistent with the presence of lupus anticoagulant, which is known to cause a paradoxical prolongation of the APTT, suggesting that there is an inhibitor affecting the coagulation pathway. In a mixing study, if a patient’s plasma is mixed with normal plasma and the APTT corrects, this usually indicates a deficiency of a coagulation factor. However, if it remains prolonged despite mixing, this supports the existence of a specific inhibitor, such as lupus anticoagulant.

Therefore, the behavior of the APTT in mixing studies serves as a crucial diagnostic indicator for identifying lupus anticoagulant, highlighting why the result of normal APTT following mixing does not align with the characteristics of this condition.