Whole Blood Clotting Test for Venom-Induced Consumptive Coagulopathies

The whole blood clotting test (WBCT) is a simple but critical bedside gross examination used in the assessment, diagnosis, and therapeutic monitoring of snakebite patients in the developing world and remote environments.1-10 Refer to the diagram below regarding instructions for performing the test. At minutes 20 and 30, the tube is gently picked up and tilted 90 degrees; a stable solid clot retained within the tube is scored “Grade 0” and indicates normal coagulation. Abnormal results are scored “Grade 1” for a partial, semisolid clot that breaks apart and detaches from the glass tube shortly after it is turned or “Grade 2” for completely incoagulable liquid blood that pours out of the tube immediately. Attempting to score the test earlier than 20 minutes will not yield accurate results due to the consumptive mechanism of the coagulopathy. Using a healthy donor as a control is ideal to confirm questionable findings.

Continue WBCT testing throughout the course of care to monitor for secondary resumption of venom-induced consumptive coagulopathy.11-13  After control of the envenomation has been achieved, reassess WBCT every 24 hours throughout the course of hospitalization. It is important to remember that the WBCT must be interpreted in the context of the larger clinical picture. If a patient has improved in all parameters except for a persistent abnormal WBCT, it may reflect an inertia in replenishment of depleted clotting factors after a severe hemotoxic envenomation.1  If the venom is active then hematocrit should continue to decrease or signs of ongoing hemolysis or bleeding should be present.

References

  1. Benjamin JM, Chippaux J-P, Sambo BT, Massougbodji A. Delayed double reading of whole blood clotting test (WBCT) results at 20 and 30 minutes enhances diagnosis and treatment of viper envenomation. J Venom Anim Toxins Incl Trop Dis. 2018;24:14. doi:10.1186/s40409-018-0151-1
  2. Sano-Martins IS, Fan HW, Castro SCB, et al. Reliability of the simple 20 minute whole blood clotting test (WBCT20) as an indicator of low plasma fibrinogen concentration in patients envenomed by Bothrops snakes. Toxicon. 1994;32(9):1045-1050. doi:10.1016/0041-0101(94)90388-3
  3. Gaus DP, Herrera DF, Troya CJ, Guevara AH. Management of snakebite and systemic envenomation in rural Ecuador using the 20-minute whole blood clotting test. Wilderness Environ Med. 2013;24(4):345-350. doi:10.1016/j.wem.2013.08.001
  4. Chippaux JP, Amadi-Eddine S, Fagot P. Diagnosis and monitoring of hemorrhage due to viper envenomation in the African savanna. Bull Soc Pathol Exot. 1999;92(2):109-113. https://www.ncbi.nlm.nih.gov/pubmed/10399601.
  5. Madaki JKA, Obilom R, Mandong BM. Clinical presentation and outcome of snake-bite patients at Zamko Comprehensive Health Centre, Langtang, Plateau State. Highland Medical Research Journal. 2004;2(2):61-68. https://www.ajol.info/index.php/hmrj/article/view/33855. Accessed December 29, 2019.
  6. Dsilva AA, Basheer A, Thomas K. Snake envenomation: is the 20 min whole blood clotting test (WBCT20) the optimum test for management? QJM. 2019;112(8):575-579. doi:10.1093/qjmed/hcz077
  7. Ratnayake I, Shihana F, Dissanayake DM, Buckley NA, Maduwage K, Isbister GK. Performance of the 20-minute whole blood clotting test in detecting venom induced consumption coagulopathy from Russell’s viper (Daboia russelii) bites. Thromb Haemost. 2017;117(3):500-507. doi:10.1160/TH16-10-0769
  8. Isbister GK, Maduwage K, Shahmy S, et al. Diagnostic 20-min whole blood clotting test in Russell’s viper envenoming delays antivenom administration. QJM. 2013;106(10):925-932. doi:10.1093/qjmed/hct102
  9. Punguyire D, Iserson KV, Stolz U, Apanga S. Bedside whole-blood clotting times: validity after snakebites. J Emerg Med. 2013;44(3):663-667. doi:10.1016/j.jemermed.2012.07.073
  10. Bawaskar HS, Bawaskar PH. Profile of snakebite envenoming in western Maharashtra, India. Trans R Soc Trop Med Hyg. 2002;96(1):79-84. doi:10.1016/s0035-9203(02)90250-6
  11. Benjamin JM, Abo BN, Brandehoff N. Review Article: Snake Envenomation in Africa. Current Tropical Medicine Reports. January 2020. doi:10.1007/s40475-020-00198-y
  12. Benjamin JM, Chippaux J-P, Tamou-Sambo B, Akpakpa OC, Massougbodji A. successful management of two patients with intracranial hemorrhage due to carpet viper (Echis ocellatus) envenomation in a limited-resource environment. Wilderness Environ Med. June 2019. doi:10.1016/j.wem.2019.04.003
  13. Lial JP. Health assessments of a military company stationed on the Maroni River in French Guiana. Med Trop . 1999;59(1):95-98. https://www.ncbi.nlm.nih.gov/pubmed/10472589.