Background <p>Hypocalcemia represents a critical physiological disturbance in trauma-related hemorrhagic shock patients. Nonetheless, the prevalence and effects of hypocalcemia remain uncertain. This study aims to explore the prevalence of hypocalcemia before blood transfusions and its related mortality in adult patients with major traumatic injuries.</p> Method <p>We conducted a systematic search through databases, including PubMed, EMBASE, Scopus, and Web of Science, from their inception until June 30, 2024. Patients with major traumatic injuries whose serum calcium was measured upon arrival at the emergency department (ED) were included. We excluded those with prior blood transfusions, pre-clinical studies, review articles, and studies without a control group. Meta-analysis using a random-effect model was performed. Heterogeneity was evaluated using Cochrane Q and I² statistics. The study’s risk of bias was assessed using the Joanna Briggs Institute’s critical appraisal checklist. Publication bias was assessed using Egger’s test and contour funnel plot visualization.</p> Results <p>Of the total, 1,984 abstracts were screened, leading to 15 studies in this review and meta-analysis. The overall prevalence of hypocalcemia upon ED arrival was 56% (95% CI 37%-74%), with high heterogeneity (<i>I</i>² 99.8%) observed. Hypocalcemia patients also had higher mortality rates than normocalcemia patients (OR 2.44, 95% CI 1.76–3.40).</p> Conclusion <p>Hypocalcemia on ED arrival is common among adult trauma patients, who also exhibit a notably high mortality rate within this demographic. We recommend the monitoring of ionized calcium levels in traumatic adult patients. Furthermore, systematically designed studies examining the optimal thresholds, treatment protocols, and outcomes should be prioritized as the focal point of research.</p> Trial registration <p>CRD42024549054 (<a href="http://www.crd.york.ac.uk/PROSPERO">http://www.crd.york.ac.uk/PROSPERO</a>).</p>