Diagnostic Tests for Hypofibrinogenemia Resulting from Green Pit Viper (Trimeresurus albolabris) Envenomation: A Simulated In Vitro Study

Abstract

Introduction: The green pit viper (GPV) Trimeresurus albolabris is found in Southeast Asia. Its venom has a thrombin-like activity that can cause hypofibrinogenemia. Fibrinogen measurement is not always available. We aimed to establish a more available diagnostic tool indicating hypofibrinogenemia caused by GPV envenomation.

Methods: This was an in vitro study, in which healthy subjects aged 20 to 45 y were enrolled. There were 2 experiments. In Experiment 1, blood samples from 1 subject had varying amounts of T albolabris venom added to determine its effect on the fibrinogen level (FL). In Experiment 2, 3 sets of blood samples were obtained from another 25 subjects. The 2 venom doses established in Experiment 1 were used on 2 sets of the samples to simulate severe (FL <1.0 g·L^-1) and mild hypofibrinogenemia (FL 1.0-1.7 g·L^-1). The third set of samples was venom-free. All samples were used for platelet counts, prothrombin time (PT)/international normalized ratio (INR)/activated partial thromboplastin time (aPTT), and 2 bedside clotting tests. Diagnostic parameters were calculated against the target FL of <1.0 g·L^-1 and <1.7 g·L^-1.

Results: Twenty-five subjects were enrolled in Experiment 2. On referencing normal cutoff values (platelet count >150,000 cells/mm³, venous clotting time <15 min, normal 20-min whole blood clotting time, INR <1.2, aPTT <30), we found abnormalities of 5, 0, 0, 3, and 22%, respectively. The highest correlation with hypofibrinogenemia was provided by PT/INR. For an FL of <1.0 g·L^-1, PT and INR revealed the highest areas under the receiver operating characteristic curve, 0.76 (95% CI, 0.55-0.97) and 0.76 (95% CI, 0.57-0.97), respectively. The highest accuracy and the highest sensitivity were provided by PT/INR.

Conclusions: PT/INR could be used as a diagnostic test for severe hypofibrinogenemia in GPV envenomation because of its high accuracy and area under the receiver operating characteristic curve.

Keywords: Trimeresurus macrops; Trimeresurus spp; prothrombin time; snakebite; venous clotting time; whole blood clotting time.