This retrospective study analyzed snakebite cases treated between June 2023 and October 2024 at The First People's Hospital of Yunnan Province (n = 63), The People's Hospital of Linxiang District (n = 28), and The First People's Hospital of Xuanwei City (n = 25). In total, 116 patients who showed signs and symptoms of hemotoxic snakebite envenoming were selected. Data collected included patient age, gender, snake species, and use of antivenom. Blood samples were collected at two time points (upon admission and within a 6 h period preceeding discharge) to assay coagulation parameters (lines 163−165 underlined in the manuscript). These parameters included prothrombin time (PT; reference range: 11.0–15.0 s), international normalized ratio (INR; 0.8–1.2), thrombin time (TT; 14.8–20.8 s), activated partial thromboplastin time (APTT; 28.0–43.5 s), fibrinogen (Fg; 2–4 g/L), fibrin degradation products (FDP; 0–5 μg/ml), and D-dimer (DD2; 0–0.5 μg/ml). All coagulation tests were conducted using the STA-R Evolution automated coagulation analyzer and compatible reagents (STAGO, France).

The use of antivenom was guided by the Chinese guidelines for management of snakebites (33), which relies on a combination of clinical presentation and available information to diagnose hemotoxic envenoming (33). The clinical signs of hemotoxic snakebite envenoming mainly include bleeding from the wound, skin petechiae, ecchymosis, gingival bleeding, hematemesis, melena, hemoptysis, and hematuria (5, 33). In severe cases, bleeding in important organs such as the brain may occur, as well as hypovolemic shock in severe cases (5, 33). Patients with comorbidities unrelated to snakebites, such as malignancies, immune disorders, pre-existing coagulation abnormalities, cardiovascular or cerebrovascular diseases, and pregnancy, were excluded from the analysis. The selection of antivenom used in the snakebite envenoming management was based on The Chinese guideline for management of snakebites. Agkistrodon halys bite uses antivenom against Agkistrodon halys envenomation (6,000 U per vial). Trimeresurus stejnegeri and Trimeresurus mucrosquamatus bites are treated with antivenom against Deinagkistrodon acutus envenomation (2,000 U per vial), as per the Chinese guideline (33) (Table 1). The two antivenoms products used in this study are produced by Shanghai Sialon Biotechnology Co., LTD. (Shanghai, China), with with the National Drug Approval number S10820180 with a 36 month validity. All the antivenoms used in the study were within their validity period and were uniformly purchased by the hospital and provided by the hospital pharmacy. In addition, as Clostridium tetani hidden in the snake's mouth poses a risk of causing tetanus, all patients were injected with tetanus immunoglobulin. According to the Visual Analog Scale (VAS) score >7, acetaminophen was given for pain relief treatment. When patients experience antivenom allergy (without shock) or still have swelling and pain after treatment with adequate antivenom, dexamethasone is given for symptomatic treatment. Patients with infection and tissue necrosis should use ceftriaxone (Table 1) (30).

The study involving human participants was reviewed and approved by the Ethics Committee of the First People's Hospital of Yunnan Province (Approval No: KHLL2024-KY087), with a validity period from January 1, 2024, to December 31, 2025. The research was conducted in accordance with the local legislation and institutional requirements. Written informed consent for participation was obtained from all patients prior to the administration of fibrinogen therapy, in accordance with hospital policy and insurer requirements. For patients treated with antivenom alone, data were analyzed retrospectively under the waiver of consent granted by the ethics committee.

This study administered treatment protocols across all three hospitals following the Chinese Guideline for the Management of Snakebites (30). As the current treatment for Fg is not recommended for snake bite patients, the use of Fg is adapted from the application of Fg in acute bleeding situations such as postpartum hemorrhage and cardiac surgery (26, 27, 31). There were thirty-three patients in the cohort who received Fg after administration of antivenom. The Fg supplementation was administered intravenously, with dosing determined according to the patient's measured Fg levels. The required dose was calculated using the formula:

In this formula, 2 g/L represents the target Fg concentration, and the factor 0.07 reflects the average plasma volume, constituting approximately 6%−8% of total body weight. Each patient received a single calculated dose based on their initial laboratory values; no subsequent dose adjustments were made based on follow-up testing. All patients receiving Fg supplementation were treated following this standardized dosing protocol. Fg (0.5 g/bottle) products were from Shanghai RAAS Blood Products Co., Ltd. and were to be stored in a light-proof environment at 2–8 °C. Before use, Fg (0.5 g/bottle) and sterilized water for injection (25 ml) were preheated to 30–37 °C. Sterilized water for injection was pre-heated by placing in a water bath at 30–37 °C and thereafter gently shaken to completely dissolve the product (vigorous shaking was avoided to prevent protein denaturation). Intravenous infusion was performed using an infusion set with a filter screening device. The drop rate was set at 60 drops per minute and Fg was used within 2 h after the administration of antivenom.

The normality of the data was assessed using the Shapiro–Wilk test and Q–Q plots. The Mann–Whitney U test was used for data with non-normal distribution, and the Student's t-test was used for data with normal distribution. The Mann–Whitney U test was applied to compare coagulation parameters (PT, INR, TT, APTT, Fg, FDP, and DD2) between the two treatment groups at admission and discharge, as these data were non-normally distributed. In our data, only the length of hospital stay conformed to the normal distribution and was expressed as mean ± standard deviation. Continuous variables are presented as medians with interquartile ranges (IQR), while categorical variables are expressed as frequencies and percentages. Moreover, 95% confidence intervals (CIs) were reported for the median values within the IQR. Data visualization was performed using GraphPad Prism 7, and statistical analyses were conducted using IBM SPSS Statistics version 21.0 (Armonk, NY, USA). A two-sided P-value of < 0.05 was considered statistically significant. All graphical representations display medians along with their corresponding 95% confidence intervals.

This study analyzed 116 patients with hematotoxic snakebites, comprising 72 males and 44 females, with a median age of 55 years (range: 13–85 years). The bites were attributed to several snake species: Trimeresurus stejnegeri (n = 17), Trimeresurus mucrosquamatus (n = 81), Agkistrodon halys (n = 14), and unidentified species (n = 4). Among the cases we included, the median time from bite to treatment was 4 (3–6) hours, and all patients received no treatment before being sent to the hospital for treatment. The occupations of the included patients mainly included farming (65.52%, 76/116), workers (mainly engaged in forestry activities; 13.79%, 16/116), unemployed (20.69%, 14/116), and others (such as tourists and herdsmen, etc.; 8.62%, 10/116). Of the total cohort, 33 patients received a combination therapy of antivenom and Fg, including 19 cases of Trimeresurus mucrosquamatus, six of Trimeresurus stejnegeri, five of Agkistrodon halys, and three unidentified. The remaining patients (n = 83) were treated with antivenom alone. Beyond treatment differences, no additional matching or grouping criteria were applied. According to the Chinese Guideline for the Management of Snakebites (30), the clinical severity of our patients was moderate. A total of 153 g of Fg was used in this study, with an average of 4.64 ± 1.40 g of Fg used per patient. Whether it was the combined treatment group or the group treated only with antivenom, the average usage of antivenom per person was 3 ± 1 vials. Fg depletion (defined as Fg < 2 g/L) was observed in 70.69% of patients (82/116), with a median Fg level of 0.82 g/L (IQR: 0.60–1.23). Among the 82 patients with Fg depletion, 62.20% (51/82) showed wound bleeding. Patients (96.23%, 51/53) with bleeding had Fg depletion, with a median Fg level of 0.65 g/L (IQR: 0.60–1.07). In comparison, patients without bleeding symptoms (37.80%, 31/82) had significantly higher Fg levels, with a median of 1.32 g/L (IQR: 1.19–1.83; P = 0.005). These findings suggest a strong association between the severity of clinical symptoms, particularly bleeding, and the extent of Fg consumption. In addition, in our cohort, the average length of hospital stay for patients treated with antivenom combined with Fg (4.88 ± 1.47 days) was shorter than that of patients treated only with antivenom (7.07 ± 2.02 days; P < 0.0001; Table 1). Baseline characteristics of the study population are presented in Table 2.

We initially compared the pre-treatment coagulation baseline parameters of patients who received antivenom combined with Fg supplementation upon admission with those who only received antivenom serum. The results showed that PT/s, APTT/s, FDP, and D-dimer levels of the Fg-treated group were significantly higher than those of the non-Fg group (P < 0.05; Table 3). However, Fg levels before treatment in the Fg-treated group was significantly lower than that of the non-Fg group (P < 0.05; Table 3). Therefore, patients with more severe coagulation dysfunction upon admission received fibrinogen supplementation.

As shown in Table 3, patients who received antivenom in combination with Fg presented with more pronounced coagulation dysfunction at admission. We then analyzed coagulation parameters at discharge between the two groups. The findings revealed that although PT (reference range: 11.0–15.0 s) and APTT (reference range: 28.0–43.5 s) remained slightly higher in the Fg-treated group compared to the non-Fg group, both values fell within normal reference limits (Table 4 and Figure 1). Furthermore, levels of Fg, FDP, and DD2 were significantly higher in the combination therapy group (P < 0.05; Table 4 and Figure 1). The Fg level is particularly interesting, as it is a critical marker of coagulation status. Fg, the most abundant coagulation factor in circulation, typically ranges between 2–4 g/L in healthy individuals (23). Following combination therapy, the hospital stay of the patients was significantly shortened (Table 2), and the Fg concentration at discharge reached 1.94 (1.52–2.20)g/L, which approached the normal physiological range and were significantly higher than those observed in patients treated with antivenom alone, whose Fg levels were 0.84 (0.68–1.17) g/L (Table 4, Figures 1, 2). the length of hospital stay for patients in the combined group was significantly shorter (4.88 ± 1.47 days) than for patients in the antivenom only group (7.07 ± 2.02 days; Table 2). This improvement may reflect improved recovery of coagulation function in cases of coagulopathy resulting from snake envenomation. Figure 2 illustrates the changes in coagulation parameters between admission and discharge among patients who received antivenom in combination with Fg.