What will the APTT result typically indicate in a patient on aspirin?

In patients who are taking aspirin, the activated partial thromboplastin time (APTT) test result typically remains normal. Aspirin functions by inhibiting platelet aggregation through the blockade of cyclooxygenase-1 (COX-1), which decreases the production of thromboxane A2, a potent promoter of platelet activation and aggregation.

The APTT assay is primarily used to evaluate the intrinsic pathway of coagulation, including factors such as VIII, IX, XI, and XII, as well as the common pathway factors I, II, V, and X. Since aspirin mainly affects platelets rather than the coagulation factors themselves, the intrinsic pathway and the common pathway remain unaffected. Therefore, the APTT does not demonstrate any prolongation or significant deviation from normal values in patients who are on aspirin therapy, leading to a normal APTT result. This reflects that while aspirin impacts platelet function, it does not alter the clotting time significantly as assessed by the APTT test.