Prehospital lactate, transfer time, and early mortality across emergency diagnostic categories

Prehospital lactate measurement is increasingly used for early risk stratification in emergency medical services. However, whether baseline metabolic derangement modifies the association between prehospital transfer time and mortality across different emergency conditions remains unclear. We evaluated the interaction between prehospital lactate levels and transfer time in relation to early mortality.

We conducted a prospective multicenter cohort study including 10,111 consecutive adults attended by advanced life support emergency medical services in Spain between February 2019 and January 2026. All patients underwent point-of-care blood gas analysis with lactate determination during the initial prehospital assessment. The primary outcome was all-cause 48-hour mortality. Multivariable logistic regression models adjusted for demographic characteristics, comorbidity burden, physiological variables, Glasgow Coma Scale score, and diagnostic category were used to assess associations between lactate, prehospital transfer time, and mortality. Lactate was modeled using restricted cubic splines, and interaction terms between lactate and transfer time were evaluated.

The median age was 68 years (interquartile range [IQR], 52-80), 61.5% of participants were male, and 48-hour mortality was 9.5%. Median prehospital lactate was 2.65 mmol/L (IQR, 1.78-4.19). Lactate concentrations and prehospital transfer times differed significantly across diagnostic categories (both p < .001). In adjusted analyses, higher lactate levels and longer prehospital transfer times were independently associated with increased mortality. A significant interaction between lactate and time was observed (p < .001), indicating that the prognostic impact of prehospital delay varied according to baseline metabolic status. Trauma and endocrine-metabolic emergencies showed the strongest lactate-dependent time sensitivity, with progressively higher mortality associated with longer prehospital transfer times at elevated lactate levels. In contrast, infectious diseases demonstrated a strong monotonic association between lactate and mortality without significant interaction with prehospital transfer time. The interaction was predominantly observed among patients with intermediate neurological impairment.

The association between prehospital transfer time and early mortality varied substantially across emergency conditions and depended on baseline metabolic status as reflected by prehospital lactate levels. Integration of point-of-care lactate assessment into early prehospital evaluation may help identify patients in whom the association between prehospital transfer time and mortality is strongest and may support future individualized transport prioritization strategies.