Utility of Thrombin Time in Management of Patients with Green Pit Vipers Bite

OBJECTIVES: GGreen pit vipers (GPV) envenomation causes consumptive coagulopathy mainly by thrombin-like enzymes. Fibrinogen levels are generally investigated to help evaluate systemic envenomation. However, tests of fibrinogen levels may not be available in every hospital. This study aimed to determine the sensitivity, specificity and accuracy for a range of various coagulation tests (20 minute whole blood clotting test (20WBCT), prothrombin time, international normalized ratio and thrombin time (TT)), comparing to the two gold standards performed in patients with GPV bite. METHODS: This was the pilot study which we retrospectively reviewed fibrinogen level results including the hospital records of 24 GPV (Trimeresurus albolabris or macrops) bite patients visiting Ramathibodi Hospital, Thailand during 2013–2017 with 65 results of fibrinogen levels. The fibrinogen levels <164 and <100 mg/dL were used as the standard cut-off points or gold standards as the abnormal low and critical levels, respectively. RESULTS: Most were male. All had local effects. For fibrinogen levels <164 and <100 mg/dL, prolonged TT had the highest sensitivity of 57.1% and 82.4%; the negative predictive value of 74.5% and 93.6%; the accuracy of 81.0% and 92.1%; and the area under a receiver operating characteristic curve of 0.762 and 0.873, respectively. For fibrinogen levels <164, unclotted 20WBCT and prolonged TT had the highest specificity and positive predictive value of 100% all. For fibrinogen levels <100, unclotted 20WBCT had the highest specificity and positive predictive value of 100% both, while prolonged TT had the specificity and positive predictive value of 95.7% and 87.5%, respectively. One patient developed isolated thrombocytopenia without hypofibrinogenemia and coagulopathy. CONCLUSIONS: Among four coagulation tests, TT was the most sensitive and accurate test to indicate hypofibrinogenemia in GPV bite patients. In case of unavailable fibrinogen levels thrombin time might be investigated to help evaluate patients’ fibrinogen status. Isolated thrombocytopenia could occur in GPV envenomation.