TEG® and RapidTEG® are unreliable for detecting warfarin- coagulopathy: a prospective cohort study

Background: Thromboelastography r (TEG) utilizes kaolin, an intrinsic pathway activator, to assess clotting function. Recent published studies suggest that TEG results are commonly normal in patients receiving warfarin, despite an increased International Normalized Ratio (INR). Because RapidTEG T includes tissue factor, an extrinsic pathway activator, as well as kaolin, we hypothesized that RapidTEG would be more sensitive in detecting a warfarin-effect. Methods: Included in this prospective study were 22 consecutive patients undergoing elective cardioversion and receiving warfarin. Prior to cardioversion, blood was collected to assess INR, Prothrombin Time, TEG, and RapidTEG. Results: INR Results: 2.8 +/- 0.5 (1.6 to 4.2). Prothrombin Time Results: 19.1 +/- 2.2 (13.9. to 24.3). TEG Results (Reference Range): R-Time: 8.3 +/- 2.7 (2-8); K-Time: 2.1 +/- 1.4 (1-3); Angle: 62.5 +/- 10.3 (55-78); MA: 63.2 +/- 10.3 (51-69); G: 9.4 +/- 3.5 (4.6-10.9); R-Time within normal range: 10 (45.5%) with INR 2.9 +/- 0.3; Correlation coefficients for INR and each of the 5 TEG variables were insignificant (P > 0.05). RapidTEG Results (Reference Range): ACT: 132 +/- 58 (86-118); K-Time: 1.2 +/- 0.5 (1-2); Angle: 75.4 +/- 5.2 (64-80); MA: 63.4 +/- 5.1 (52-71); G: 8.9 +/- 2.0 (5.0-11.6); ACT within normal range: 9 (40.9%) with INR 2.7 +/- 0.5; Correlation coefficients for INR and each of the 5 RapidTEG variables were insignificant (P > 0.05). Conclusions: 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. The false-negative rate for detecting warfarin coagulopathy with either test is unacceptable. The lack of correlation between INR and all TEG and RapidTEG components further indicates that these methodologies are insensitive to warfarin effects. Findings suggest that intrinsic pathway activation may mitigate detection of an extrinsic pathway coagulopathy.