Association between prognosis and calcium trajectories in patients with spinal cord injury based on MIMIC-IV data

To investigate the correlation between dynamic changes in serum calcium levels and prognosis in patients with spinal cord injury (SCI), and to provide a reference for clinical assessment of disease severity and prognosis in SCI patients. Data for this study were extracted from version 3.0 of the MIMIC-IV database, including 699 adult patients diagnosed with SCI. Group-based trajectory modeling (GBTM) was used to analyze serum calcium test data, classifying patients into different calcium trajectory types. Baseline characteristics among different trajectory groups were compared using the Kruskal-Wallis test, analysis of variance, and chi-square test. Kaplan-Meier survival curves were plotted with log-rank tests, and a Cox proportional hazards regression model was constructed to analyze the independent impact of calcium trajectories on patient prognosis. Subgroup analyses were further performed to evaluate the robustness of the results. The C-statistic and Net Reclassification Improvement (NRI) were used to evaluate the optimization effect of combining calcium trajectories with conventional prognostic scoring systems on the predictive model for ICU mortality risk in patients with SCI. Trajectory analysis classified serum calcium trajectories into two types: Class 1 (244 cases) characterized by "a steep decline in serum calcium ion levels" and Class 2 (455 cases) characterized by "a slow but persistent decline in serum calcium ion levels." Baseline characteristics showed that Class 1 patients had significantly longer ICU stay, total hospital stay, ICU survival time, and in-hospital survival time compared to Class 2 (P < 0.05). Survival analysis indicated that Class 1 patients had significantly lower 30-day and 60-day all-cause mortality in the ICU than Class 2 (P < 0.05). Cox regression analysis revealed that after adjusting for confounding factors such as age, gender, diabetes mellitus, and hypertension, Class 2 remained an independent risk factor for increased mortality (P < 0.05). Subgroup analyses showed no significant interaction between the results and gender, age, or diabetes mellitus (P > 0.05), but the elevated mortality risk in Class 2 was more pronounced in patients with hypertension (HR = 3.282, P = 0.027). Calcium trajectories can enable 23.6-27.4% of patients to obtain more accurate risk stratification, and in particular, significantly improve the ability to identify high-risk patients among those with the death outcome (Event NRI = 0.185-0.213). The dynamic change trajectory of serum calcium in patients with SCI is closely associated with their prognosis. The trajectory type characterized by "slow but continuous decline in serum calcium ion levels" indicates a significantly increased risk of ICU mortality in patients. Serum calcium trajectory can not only serve as a potential biomarker for evaluating the prognosis of SCI patients but also provide significant incremental predictive value for conventional prognostic scoring systems, thereby offering references for clinical stratified management and personalized treatment in the ICU. However, the results of this study are only applicable to critically ill SCI patients admitted to the ICU.