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Prothrombin activation in eastern tiger snake bite
John Desmond Parkin1, Kamal Ibrahim, Raymond John Dauer
1Division of Laboratory Medicine, Austin and Repatriation Medical Centre, Melbourne, Victoria, Australia. des.parkin@armc.org.au
Aims:
To perform ex vivo studies in eastern tiger snake envenomation which define the haemostatic events associated with prothrombin activation.
Method:
Serial studies were performed on plasma from six individuals with evidence of eastern tiger snake envenomation. These analyses were particularly directed to fibrinogen levels, F1 + 2, TAT and evidence of fibrinolysis.
Results:
There was a substantial rise in F1 + 2 and thrombin-antithrombin (TAT) complexes in all cases, even with minimal evenomation. In some cases the molar ratio of F1 + 2 and TAT was reduced from the relationship normally seen in vitro and ex vivo in clinical thrombosis. There was a dramatic fall in factor V and VIII levels which occurred 4-6 hours before the decline in prothrombin and AT3. This related in time to a fall in alpha2AP and plasminogen. Protein C levels also declined dramatically but many hours after presentation.
Conclusions:
F1 + 2 and TAT are sensitive markers of tiger snake evenomation. In some patients with massive prothrombin activation, the common mechanism for TAT clearance may be altered or overwhelmed. Conversely, the renal clearance of the smaller F1 + 2 may be enhanced. In the absence of thrombocytopaenia, which is a very sensitive marker of DIC, the fall in labile factors with tiger snake envenomation is significantly contributed to by proteolytic digestion of clotting factors.