The PTT(Partial Thromboplastin Time) test is used to investigate unexplained bleeding or clotting. The partial thromboplastin time (PTT) test is a blood test that is done to investigate bleeding disorders and to monitor patients taking an anticlotting drug (heparin). Measuring the partial thromboplastin time helps to assess which specific clotting factors may be missing or defective. This test is used to evaluate hemostasis,liver disease or defective clotting factor.