Low serum calcium is a novel predictor of unfavorable prognosis after traumatic brain injury

Background:Accurate and convenient serological markers for prognosis after traumatic brain injury (TBI) are still lacking. We aimed to explore the predictive value of serum calcium for prognosing outcomes within 6 months after TBI. Methods:In this multicenter retrospective study, 1255 and 719 patients were included in development and validation cohorts, respectively, and their 6-month prognoses were recorded. Serum calcium was measured through routine blood tests within 24 h of hospital admission. Two multivariate predictive models with or without serum calcium for prognosis were developed. Receiver operating characteristics and calibration curves were applied to estimate their performance. Results:The patients with lower serum calcium levels had a higher frequency of unfavorable 6month prognosis than those without. Lower serum calcium level at admission was associated with an unfavorable 6-month prognosis in a wide spectrum of patients with TBI. Lower serum calcium level and our prognostic model including calcium performed well in predicting the 6month unfavorable outcome. The calcium nomogram maintained excellent performance in discrimination and calibration in the external validation cohort. Conclusions:Lower serum calcium level upon admission is an independent risk factor for an unfavorable 6-month prognosis after TBI. Integrating serum calcium into a multivariate predictive model improves the performance for predicting 6-month unfavorable outcomes.