A 50-year-old man has been on heparin for the past 7 days. Which combination of the tests is expected to be abnormal?

Heparin is an anticoagulant that primarily affects the intrinsic pathway of the coagulation cascade, which is assessed through the activated partial thromboplastin time (APTT). In patients receiving heparin, it is expected for the APTT to be prolonged due to the drug's mechanism of action, which enhances the activity of antithrombin III, leading to the inhibition of thrombin and factor Xa.

Prothrombin time (PT) is usually less affected by heparin unless there are other coexisting factor deficiencies or conditions such as liver disease. However, in practical scenarios, especially with longer heparin therapy, changes in the PT can also occur, particularly if there is also some underlying coagulopathy or if other factors are involved.

Thrombin time (TT) measures the time taken for a fibrin clot to form in plasma after the addition of thrombin; this can also be prolonged in cases of heparin use, especially if the patient has other underlying issues such as low fibrinogen levels or the presence of heparin-induced thrombocytopenia (HIT), which can lead to altered fibrinogen levels.

Given the interaction of heparin with multiple components of the coagulation