Diagnostic characteristics of the 20-minute whole blood clotting test in detecting venom-induced consumptive coagulopathy following carpet viper envenoming

Author summaryBites by the West African carpet viper (Echis ocellatus) are very common in the savannah regions of west Africa and envenomed victims usually develop a bleeding syndrome. Routine laboratory coagulation tests are unavailable in health facilities where most snakebite victims are treated. We conducted analysis of 20-minute whole blood clotting tests (20WBCT) performed on snakebite patients in Kaltungo General Hospital, Nigeria who presented within 24 hours of the bite and who brought a dead snake along for snake identification, and we assessed its ability to detect venom induced consumptive coagulopathy (defined as an INR & GE;1.4). In our cohort of 121 patients, the 20WBCT had a sensitivity of 87% and a specificity of 50% in detecting VICC. Performing the 20WBCT increased the probability of detecting VICC among our study participants, and it was useful in identifying patients with persistent and rebound coagulopathies who may require extra doses of antivenom. Our findings show that the 20WBCT is a simple, cheap, and easily accessible bedside test with a high sensitivity for the detection of patients with VICC following carpet viper envenoming in North-eastern Nigeria. IntroductionEnvenoming by Echis spp. (carpet or saw-scaled vipers) causes haemorrhage and coagulopathy and represents a significant proportion of snakebites in the savannah regions of West Africa. Early diagnosis of envenoming is crucial in the management of these patients and there is limited evidence on the utility of the 20-minute whole blood clotting test (20WBCT) in diagnosing venom-induced consumptive coagulopathy (VICC) following envenoming by Echis ocellatus. MethodsA prospective observational cohort study was conducted at the Kaltungo General Hospital in North-eastern Nigeria from September 2019 to September 2021. Standardised 20WBCTs were conducted by trained hospital staff and citrated plasma samples were collected at numerous timepoints. Prothrombin time (PT) and international normalised ratio (INR) were determined using a semi-automated analyser and INR values were calculated using international sensitivity indices (ISI). The sensitivity, specificity, positive predictive values (PPV), negative predictive values (NPV), and likelihood ratios of the 20WBCT compared to an INR & GE; 1.4 were calculated, alongside 95% confidence intervals. ResultsWe enrolled 121 patients into our study, with a median age of 26 (18.0-35.0) years and a male predominance (75.2%). The 20WBCT was positive (abnormal) in 101 out of 121 patients at timepoint 0h, of which 95 had an INR & GE; 1.4, giving a sensitivity of 87.2% (95%CI 79.4-92.8). Among patients with a negative 20WBCT (normal), six had an INR < 1.4 giving a specificity of 50% (95%CI 21.1-78.9%). The positive and negative likelihood ratios were 1.7 (95%CI 1.6-1.9) and 0.3 (95%CI 0.1-0.4) respectively. ConclusionThe 20WBCT is a simple, cheap, and easily accessible bedside test with a high sensitivity for the detection of patients with venom induced consumptive coagulopathy (VICC) following envenoming by E. ocellatus, although false positives do occur. Repeated 20WBCTs can identify patients with new, persistent, and rebound coagulopathy.

Automated summary

Bites by the West African carpet viper often lead to a bleeding syndrome. In this study, the researchers analyzed the use of the 20-minute whole blood clotting test (20WBCT) for detecting venom-induced consumptive coagulopathy (VICC) in snakebite patients. The 20WBCT showed a high sensitivity of 87% and a specificity of 50% for detecting VICC. It is a simple and cost-effective bedside test that can be used in the diagnosis of VICC in North-eastern Nigeria.