Diagnostic 20-min whole blood clotting test in Russell’s viper envenoming delays antivenom administration G.K. ISBISTER 1,2 , K. MADUWAGE 1,2 , S. SHAHMY 2 , F. MOHAMED 2,3 , C. ABEYSINGHE 4,5 , H. KARUNATHILAKE 4,5 , C.A. ARIARATNAM 6 and N.A. BUCKLEY 2,3 From the 1 Department of Clinical Toxicology and Pharmacology, Calvary Mater Newcastle and School of Medicine and Public Health, University of Newcastle, Newcastle, NSW, Australia, 2 South Asian Clinical Toxicology Research Collaboration, University of Peradeniya, Peradeniya, Sri Lanka, 3 Medical Professorial Unit, Prince of Wales Hospital Medical School, University of New South Wales, Sydney, NSW, Australia, 4 Faculty of Medicine, University of Peradeniya, Peradeniya, Sri Lanka, 5 Polonnaruwa General Hospital, North Central Province, Polonnaruwa, Sri Lanka and 6 Department of Clinical Medicine, Faculty of Medicine, University of Colombo, Colombo, Sri Lanka Address correspondence to Dr G. Isbister, Department of Clinical Toxicology and Pharmacology, Calvary Mater Newcastle, Edith St, Waratah, NSW 2298, Australia. email: geoff.isbister@gmail.com Received 26 February 2013 and in revised form 31 March 2013 Summary Background: The 20-min whole blood clotting test (WBCT20) is widely used for the identification of coagulopathy in snake envenoming, but its performance in practice has not been evaluated. Aim: We aimed to investigate the diagnostic utility of the WBCT20 for coagulopathy in Russell’s viper envenoming. Design: Prospective observational study. Methods: Adult patients with snake envenoming were recruited. Age, sex, bite information, clinical effects, serial WBCT20 and antivenom treatment were recorded. Definite Russell’s viper envenoming was confirmed with venom specific enzyme im- munoassay. We assessed sensitivity of admission WBCT20 to coagulopathy (international normalized ratio, INR > 1.5) in Russell’s viper envenoming, the specificity of negative WBCT20 in non-envenomed patients and directly compared paired WBCT20 and INR. Results: Admission WBCT20 was done in 140 Russell’s viper bites with coagulopathy and was positive in 56/140 [sensitivity 40% (95% confidence interval (CI): 32–49%)]. A negative WBCT20 led to delayed antivenom administration [WBCT20Àve tests: median delay, 1.78 h (interquartile range (IQR): 0.83–3.7 h) vs. WBCT20 + ve tests: median delay, 0.82 h (IQR: 0.58–1.48 h); P = 0.0007]. Delays to antivenom were largely a consequence of further WBCT20 being performed and more common if the first test was negative (41/84 vs. 12/56). Initial WBCT20 was negative in 9 non- envenomed patients and 48 non-venomous snake- bites [specificity: 100% (95% CI: 94–100%)]. In 221 paired tests with INR > 1.5, the WBCT20 was positive in 91(41%). The proportion of positive WBCT20 only increased slightly with higher INR. Conclusions: In clinical practice, the WBCT20 has low sensitivity for detecting coagulopathy in snake envenoming and should not over-ride clin- ical assessment-based decisions about antivenom administration. There is an urgent need to develop a simple bedside test for coagulopathy in snake envenoming. ! The Author 2013. Published by Oxford University Press on behalf of the Association of Physicians. All rights reserved. For Permissions, please email: journals.permissions@oup.com Page 1 of 8 Q J Med doi:10.1093/qjmed/hct102 QJM Advance Access published May 14, 2013 by guest on May 15, 2013 http://qjmed.oxfordjournals.org/ Downloaded from