In a patient with prolonged PTT, what can indicate the presence of a circulating anticoagulant?

In the scenario of a patient with a prolonged Partial Thromboplastin Time (PTT), the presence of a circulating anticoagulant can be suggested by the behavior of the PTT in a corrected PTT test conducted under specific conditions. When the PTT is prolonged due to the presence of an inhibitor such as a circulating anticoagulant, incubating a sample of the patient's plasma with normal plasma may not result in correction of the PTT.

In contrast, if the PTT is corrected upon incubation, it indicates that the prolonged time was due to a factor deficiency, rather than an inhibitor. Therefore, observing a failure to correct the PTT upon incubation is a strong indicator that a circulating anticoagulant is present.

The other options do not directly relate to identifying the presence of a circulating anticoagulant in this context. For instance, increased platelet count does not influence PTT; rather, it pertains to platelet function and coagulopathy. The normal PT ratio indicates that the extrinsic pathway is functioning properly and does not provide information about intrinsic pathway abnormalities. Normal plasma addition refers to replacing the patient's plasma with normal plasma to observe adjustments in coagulation levels, but without the specific context of incubation, it doesn't clearly demonstrate the presence of an