In a prolonged aPTT that does not correct with mixing with normal plasma, which is most likely?

In a prolonged aPTT that does not correct with mixing with normal plasma, which is most likely?

• A. Factor deficiency
• B. Inhibitor of other anticoagulants
• C. Vitamin K deficiency
• D. Liver disease

Answer: (B)

When a prolonged aPTT does not shorten after mixing patient plasma with normal plasma, it points to an inhibitor present in the patient’s blood that interferes with the clotting process. Mixing with normal plasma supplies the missing factors if the problem were a simple deficiency, so that scenario would correct the test. An inhibitor, on the other hand, actively prevents correction by neutralizing factors or interfering with the assay itself. This is why an inhibitor is most likely in this scenario. If the issue were vitamin K deficiency, adding normal plasma would supply the vitamin K–dependent factors and the aPTT would typically correct. Liver disease can prolong the test through reduced factor production, but without an inhibitor, mixing often leads to some degree of correction. The non-correction pattern is classically associated with circulating inhibitors such as lupus anticoagulant or a factor-specific inhibitor, making that option the best fit.

When a prolonged aPTT does not shorten after mixing patient plasma with normal plasma, it points to an inhibitor present in the patient’s blood that interferes with the clotting process. Mixing with normal plasma supplies the missing factors if the problem were a simple deficiency, so that scenario would correct the test. An inhibitor, on the other hand, actively prevents correction by neutralizing factors or interfering with the assay itself.

This is why an inhibitor is most likely in this scenario. If the issue were vitamin K deficiency, adding normal plasma would supply the vitamin K–dependent factors and the aPTT would typically correct. Liver disease can prolong the test through reduced factor production, but without an inhibitor, mixing often leads to some degree of correction. The non-correction pattern is classically associated with circulating inhibitors such as lupus anticoagulant or a factor-specific inhibitor, making that option the best fit.