What implication does a prolonged APTT have if it normalizes after mixing?

When a prolonged activated partial thromboplastin time (APTT) normalizes after mixing patient plasma with normal plasma, it suggests the presence of a factor deficiency rather than an inhibitor. In this scenario, the mixing study dilutes the patient's plasma with an equal volume of normal plasma, which has all the necessary clotting factors present. If the prolonged APTT resolves after this dilution, it indicates that the original sample likely had a deficient factor that is adequately supplied by the normal plasma.

In contrast, if there were an inhibitor present, such as a factor inhibitor, mixing would not correct the prolonged APTT because the inhibitor would still act against the factors supplied by the normal plasma. This differentiation is crucial for diagnosing the underlying coagulation issue.

Understanding this interplay of mixing studies allows healthcare professionals to determine whether the cause of coagulopathy is due to deficiencies in coagulation factors or the presence of inhibitors, guiding further testing and treatment approaches effectively.