This study aimed to evaluate the predictive accuracy of baseline lactate levels and the modified age-adjusted quick Sequential Organ Failure Assessment (qSOFA) score in forecasting mortality in critically ill pediatric patients.

A retrospective single-center analysis was conducted on patients aged ≤18 years admitted to the intensive care unit (ICU) between January 1, 2019, and December 31, 2023. The predictive performance of lactate levels at baseline and that of the modified age-adjusted qSOFA score were compared in terms of mortality.

Among 1156 patients (median age: 20.2 months; mortality rate: 6.2 %), non-survivors exhibited significantly higher baseline lactate levels (3.7 [2.4–4.9] vs. 2.1 [1.4–3.4] mmol/L, *p* < 0.01) and modified age-adjusted qSOFA scores (3 (Bulgarelli et al., 2020; Filho et al., 2016a; Issa et al., 2021) vs. 1 [0–2], *p* < 0.01) compared to survivors. The baseline lactate level exhibited a predictive value of 0.699(sensitivity: 59.7 %; specificity: 74.9 %). The modified age-adjusted qSOFA score showed greater predictive capability than baseline lactate levels in critically ill pediatric patients; nevertheless, it is constrained by limited specificity. The predictive value of baseline lactate level paired combined with the modified age-adjusted qSOFA score was similar to that of the modified age-adjusted qSOFA score alone. Specifically, when the area under the Receiver Operating Characteristic (ROC) curve reached 0.836, the specificity enhanced with the integration of these two indicators. However, lactate levels and the modified age-adjusted qSOFA score did not influence clinical decision-making in critically ill pediatric patients, as demonstrated by subgroup analysis according to different baseline lactate concentrations.

Baseline lactate and the modified age-adjusted qSOFA score had a low-accuracy ability to predict mortality in critically ill children. Although the combination of lactate and the modified age-adjusted qSOFA score appears to enhance predictive ability, it remains an insufficient predictor for making definitive clinical decisions in critically ill children.