Warfarin Clotting Time was 289 ± 78 seconds in the warfarin-treated plasma, with a normal value of 38–79 seconds. Of relevance, a study by Rumph demonstrated that Thromboelastometry (ROTEM®), using calcium chloride and tissue factor activation, showed marked increases in Clotting Time (analogous to TEG R-Time), when warfarin-treated plasma was analyzed. Recent literature suggests that viscoelastic study results vary, when there is a warfarin-effect, depending on the activator being used. More specifically, kaolin is an intrinsic activator therefore coagulation time (R-Time) is sensitive to heparin. Thus, depending on the activator, this may correspond to clotting times measured by aPTT (intrinsic process) or PT (extrinsic process)”. In other words, several different reagents can be used: Kaolin – Intrinsic Activator Tissue Factor – Extrinsic Activator and others. Several review articles emphasized the importance of knowing the “assay variant” (clotting activator) utilized in a given set of studies. It is important to recognize that with the TEG assay, kaolin or celite, as factor XII activators, or tissue factor may be used to enhance clot formation. The R-Time (clotting time) is the time in minutes from clot activation until the graphic amplitude is 2 mm, that is, until the first detectable levels of fibrin clot formation. Thromboelastography (TEG®) assesses the viscoelastic properties of blood during the clotting process. In that study, warfarin was found to be associated with a significant increase in trauma-related mortality, even after adjusting for confounding co-morbidities. A publication by Dossett indicates that warfarin use is common among injured patients and its prevalence has increased each year since 2002. The prevalence of warfarin use in the United States is unknown, however the Food and Drug Administration estimates that more than 31 million prescriptions for warfarin were written in 2004. Findings suggest that intrinsic pathway activation may mitigate detection of an extrinsic pathway coagulopathy. The lack of correlation between INR and all TEG and RapidTEG components further indicates that these methodologies are insensitive to warfarin effects. The false-negative rate for detecting warfarin coagulopathy with either test is unacceptable. TEG, using kaolin activation, and RapidTEG, with kaolin and tissue factor activation, were normal in a substantial percent of warfarin patients, despite an increased INR. Prior to cardioversion, blood was collected to assess INR, Prothrombin Time, TEG, and RapidTEG. Included in this prospective study were 22 consecutive patients undergoing elective cardioversion and receiving warfarin. Because RapidTEG™ includes tissue factor, an extrinsic pathway activator, as well as kaolin, we hypothesized that RapidTEG would be more sensitive in detecting a warfarin-effect. Recent published studies suggest that TEG results are commonly normal in patients receiving warfarin, despite an increased International Normalized Ratio (INR). Thromboelastography® (TEG) utilizes kaolin, an intrinsic pathway activator, to assess clotting function.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |