Utility of non-specific symptoms in early detection of Russell's viper () envenoming following snakebite in rural Sri Lanka.

Introduction

Early diagnosis of systemic snake envenoming is essential for prompt antivenom treatment. The commonly used 20-min whole blood clotting test has poor sensitivity. We investigated the diagnostic utility of non-specific systemic symptoms alone or with the 20-min whole blood clotting test in detecting Russell's viper () envenoming following a snakebite.

Methods

We included snakebite patients admitted to a Sri Lankan hospital from July 2020 to June 2021. Snakebites were authenticated by snake identification or venom assays. Clinical assessments, whole blood clotting tests and an international normalized ratios were performed on admission. Non-specific systemic symptoms were vomiting, headache or abdominal pain. Systemic envenoming was defined as venom-induced consumption coagulopathy (international normalized ratio >1.5), neurotoxicity, or acute kidney injury.

Results

There were 216 snakebites: 76 Russell's viper, 89 hump-nosed viper and 51 non-venomous snakebites. Sixty-three (29%) had non-specific systemic symptoms on admission, most commonly Russell's viper bites (53/76; 70%), compared to 10/89 (11%) hump-nosed viper bites and no non-venomous snakebites. The sensitivity of non-specific symptoms in diagnosing Russell's viper envenoming in all snakebites varied, with abdominal pain having the best sensitivity of 63% (95% CI: 51-74%) and the presence of any non-specific symptom had a sensitivity of 72% (95% CI: 60-81%). The 20min whole blood clotting test had a sensitivity of 60% (95% CI: 48-71%). The combined test of abdominal pain OR a positive 20-min whole blood clotting test had a sensitivity of 82% (95% CI: 72-90%) and a specificity of 99% (95% CI: 95-100%) for Russell's viper envenoming in all snakebites, while any non-specific symptom OR a positive 20-min whole blood clotting test had a sensitivity of 88% (95% CI: 79-94%) and a specificity of 91% (95% CI: 85-94%).

Discussion

Non-specific systemic symptoms were common in Russell's viper bites, but not in hump-nosed viper bites. Non-specific symptoms OR a positive 20-min whole blood clotting test had an excellent sensitivity and specificity for Russell's viper envenoming. Further studies are required for different snake species and geographical regions.

Conclusion

In low-income settings with only access to a 20-min whole blood clotting test, the addition of non-specific symptoms, particularly abdominal pain, in snakebite diagnosis will improve early antivenom treatment.