One potential cause of elevated aPTT levels is the use of certain medications. Certain anticoagulants such as warfarin (Coumadin), heparin, and low-molecular-weight heparins may increase your risk for an abnormally high aPTT result. Other drugs that may contribute to elevated levels include aspirin, nonsteroidal anti-inflammatory drugs (NSAIDs), and immunosuppressive medications. Additionally, genetic factors such as deficiencies in certain clotting factors can also lead to abnormal aPTT results.