Predictors and nomogram for amputation risk in pit viper snakebite envenoming at hospital admission

Pit viper snakebite envenoming remains a critical global health challenge, with tissue necrosis and subsequent amputation posing significant morbidity despite antivenom availability. Existing prediction tools lack integration of dynamic laboratory parameters and iatrogenic factors, limiting their clinical utility. A retrospective cohort study analyzed 1,527 pit viper snakebite envenoming cases from the People's Hospital of Lichuan City (2012-2025). Data encompassed demographics, bite characteristics, treatment timelines, and laboratory parameters (neutrophil-to-lymphocyte ratio [NLR], D-dimer, fibrinogen [FIB]). Univariate and multivariate logistic regression analyses identified independent predictors, and a nomogram was constructed using R software. Model performance was evaluated via area under the curve (AUC), calibration curves, Hosmer-Lemeshow tests, and decision curve analysis (DCA). Key predictors included tourniquet misuse (OR = 15.45, 95% CI: 9.27-25.77), antivenom injection time (> 6 h; OR = 11.82, 95% CI: 7.18-19.45), the time from injury to admission (> 6 h; OR = 3.90, 95% CI: 2.46-6.20). Elevated NLR (OR = 1.25) and D-dimer (OR = 1.12) predicted amputation risk, whereas higher FIB demonstrated a non-significant protective trend (OR = 0.79, P = 0.090). The nomogram demonstrated exceptional discrimination (AUC: 0.893 training, 0.881 testing) and calibration (Hosmer-Lemeshow P > 0.14), with high sensitivity (90-93%) and moderate specificity (68-72%). DCA confirmed clinical utility across risk thresholds (2-100%). This study highlights the interplay of temporal and laboratory parameters in amputation risk. The nomogram provides a robust tool for early risk stratification, emphasizing timely antivenom use and standardized first aid. This model offers a valuable reference for the implementation of prompt preventive and therapeutic interventions.