Background
Patients with copperhead snakebite tend to have less severe hematologic abnormalities than with other pit viper bites, yet those laboratory studies are routinely ordered.
Objective
The purpose of this study was to characterize the incidence of abnormal hematologic studies in patients with copperhead bite, and to determine whether these abnormalities are associated with clinically significant bleeding.
Methods
Using established methodology for retrospective chart review, we performed blinded, dual chart abstraction for all patients who had verified copperhead bite presenting to a tertiary care emergency department from April 2009 to October 2012. Data collected included platelet count, serum fibrinogen, prothrombin time, partial thromboplastin time, predefined clinically significant bleeding, death, and antivenom use. Confidence intervals of proportions were calculated using the Wilson score interval.
Results
Ninety-four patients presented with copperhead bite during the 41-month study period. The mean age was 37 years (SD 21 years); 51% (48 of 94) were male. In all, 98% of patients (92 of 94) had at least a single set of the studies performed. Hematologic abnormalities occurred in 27% (95% CI: 0. 21–0.39) of these patients: 4% (4 of 92) had thrombocytopenia (range 96–147 ×109/L); 18% (17 of 92) had hypofibrinogenemia (range 142–212 mg/dL); 5% (5 of 92) had an elevated prothrombin time (range 13.4–14.1 s); and 3% (3 of 92) had an elevated partial thromboplastin time (range 38.5–39.3 s). No clinically significant bleeding or death was observed (0%, 95% CI: 0–0.04). Ninety percent of patients received antivenom therapy.
Conclusions
Although a substantial proportion of patients had a measurable hematologic abnormality, no clinically significant bleeding occurred. Routine hematologic tests to detect significant bleeding in all patients with copperhead snakebite and access to antivenom therapy are not warranted. Which patients will benefit from testing, and the role of these tests as prognostic markers of systemic or local tissue symptoms, remains unclear.