Clinical and Laboratory Features Distinguishing Between and Envenomation

Background: There are 6 species of venomous snakes in Taiwan. Two of them, () and (), can cause significant coagulopathy. However, a significant proportion of patients with snakebites cannot identify the correct snake species after envenomation, which hampers the application of antivenom. Hence, the differential diagnosis between the two snakebites by clinical presentations is important. This study aims to compare their clinical and laboratory features for the purpose of differential diagnosis between the two snakebites.

Methods: We retrospectively reviewed the medical records of patients who arrived at the emergency department due to or envenomation, between 2003 and 2016, in one medical center in eastern Taiwan. Since these snakebites are rare, we also included 3 cases reported from another hospital in central Taiwan.

Results: In total, 15 patients bitten by and 12 patients by were analyzed. Hemorrhagic bulla formation and the need for surgical intervention only presented for envenomation cases (Both 53.3% vs. 0.0%,  = 0.003). As to laboratory features, lower platelet counts (20.0 ×  10/μL [interquartile range, 14-66 × 10/μL] vs. 149.0 × 10/μL [102.3-274.3 × 10/μL],  = 0.001), lower D-dimer level (1423.4 μg/L [713.4-4212.3 μg/L] vs. 12,500.0 μg/L [2351.4-200,000 μg/L],  = 0.008), higher proportion of patients with moderate-to-severe thrombocytopenia (platelet count < 100 × 10/μL) (80% vs. 16.7%, odds ratio (OR) = 20.0, 95% CI, 2.77-144.31;  = 0.002), and lower proportion of patients with extremely high D-dimer (> 5000 ng/mL) (16.7% vs. 66.7%, adjusted OR = 0.1 (95% CI, 0.01-0.69;  = 0.036) were found among cases of envenomation compared to envenomation. The combination of hemorrhagic bulla, thrombocytopenia, and a lack of extremely high D-dimer had good discriminatory power (area under the curve (AUC) = 0.965; 95% CI, 0.904-1.00) for distinguishing from envenomation.

Conclusions: The presentation of moderate to severe thrombocytopenia (platelet count < 100 × 10/μL) and hemorrhagic bulla formation may indicate envenomation. However, the envenomed patient with extremely high D-dimer levels may indicate a envenomation. These findings may help diagnose and select the right antivenom in patients with unknown snakebites who present significant coagulopathy.