Characterization of anemia following rattlesnake envenomation in Arizona: a retrospective observational study

Introduction: Rattlesnakes in the southwestern United States possess hemotoxic venom associated with coagulopathy and bleeding. While the two complications are related, they are distinct entities, and no known study has evaluated the phenomenon of venom-induced anemia. Methods: A chart review was performed using electronic health records from the Arizona Poison and Drug Information Center between January 1^st, 2017 and December 31^st, 2022. Included charts were characterized by the presence or absence of anemia (hemoglobin <100 g/L), and clinical and demographic information were compared between the two subgroups. Results: A total of 800 records were found within the time period, of which 705 patient records were included. Female sex was significantly associated with increased anemia rates (OR 2.23 [95% CI: 1.14–4.36]; P = 0.02), but age was not (OR 0.99 [95% CI: 0.98–1.00]; P = 0.13). When adjusting for age/sex, the prevalence of anemia was associated with dual anticoagulant/antiplatelet therapy (OR 55.4 [95% CI: 3.10-993]; P = 0.006), visible inpatient bleeding (OR 10.1 [95% CI: 2.87–35.7]; P <0.001) and ecchymosis extending more than half an extremity (OR 6.17 [95% CI: 3.06–12.4]; P <0.001), among others. Discussion: Anemia in the setting of rattlesnake envenomation is likely multifactorial, and potentially due to erythrocyte sequestration, occult bleeding, and erythrocyte destruction, both direct and indirect. Patients with anemia were shown to have higher rates of coagulopathy, specifically thrombocytopenia, and derangements to the international normalized ratio. Conclusions: Patients on dual anticoagulant/antiplatelet or chronic non-steroidal anti-inflammatory drug therapy were found to have increased rates of anemia. Thrombocytopenia and an increased international normalized ratio were associated with higher rates of anemia when adjusting for age and sex.