Clotting Assay Predicts Patient Transfusion Needs

The new test, developed by researchers at the University of Colorado School of Medicine, modifies thrombelastography (TEG)--a test that measures the viscoelastic properties of whole blood to determine the ability of blood to clot--by adding tissue plasminogen activator (tPA) to the blood sample. As tPA saturates endogenous inhibitors, systemic hyperfibrinolysis occurs, which can help stratify the underlying degree of shock and identify early coagulation changes in order to predict progression to massive transfusion.

To test this hypothesis, the researchers analyzed blood samples from 324 trauma patients, of which 17% required a massive blood transfusion. Trauma activations were analyzed using rapid TEG and the modified TEG-tPA test. Clinical scores, which included shock index, assessment of blood consumption, and trauma-associated severe hemorrhage were then compared with TEG measurements to predict the need for massive transfusion, using areas under the receiver operating characteristic curves.

The results showed that rapid TEG and tPA-TEG parameters were significantly different in all massive transfusion patients compared to non-massive transfusion patients. Low-dose tPA lysis at 30 minutes had the largest the area under the receiver operating characteristic curve for prediction of massive transfusion, similar to the international normalized ratio (INR) of prothrombin time. When the tPA-TEG assay was used together with INR, it improved identification of patients in need of transfusion by 40%, and identified 97% of patients who did not, thereby preventing unnecessary transfusions. The study was published on May 15, 2017, in JACS.

“The tPA-TEG identifies trauma patients who require massive transfusion efficiently in a single assay that can be completed in a shorter time than other scoring systems, which has improved performance when combined with international normalized ratio,” concluded lead author Hunter B. Moore, MD, of the department of surgery. “This new method is consistent with our understanding of the molecular events responsible for trauma-induced coagulopathy.”

TEG is performed by gently rotating a blood sample through approximately 5º six times a minute in order to imitate sluggish venous flow and to activate coagulation. The speed at which the sample coagulates on a thin wire probe depends on the activity of the plasma coagulation system, platelet function, fibrinolysis, and other factors. The patterns of changes in strength and elasticity in the clot provide information about how well the blood can perform hemostasis, and how well or poorly different factors are contributing to clot formation.