From Dr. King: We are encountering with increasing frequency requests from hematologists to perform mixing studies on patients that are known to be on some form of anticoagulation. My question is regarding the utility of doing such testing. Another aspect to the question is whether you can do testing for a prolonged PTT when the patient is known to be on warfarin or evaluate a prolonged PT in a patient known to be on therapeutic doses of heparin. I wonder whether others are encountering this same request and would appreciate yours and their thoughts. Thanks.
Hello, and thank you for your question. The recently released target-specific oral anticoagulants (TSOACs) variably prolong the PT and PTT, rendering their results uninterpretable and hopelessly interfering with mixing studies. See Favaloro EJ, Lippi G. The new oral anticoagulants and the future of haemostasis laboratory testing Biochemia Medica 2012;22:329-41 for a comprehensive review. Likewise, there is little that one can do with warfarin specimens, as the warfarin effect on the vitamin K dependent factors is irreversible. It is possible to neutralize unfractionated heparin using Hepzyme® or polybrene (Hepsorb®) to perform a PTT or a PT mixing study. I am curious about why your hematologists request PT mixes, as the PT mixing study provides limited diagnostic information.