Prognostic value of admission ionized calcium and acidosis in severely injured trauma patients

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The association between ionized calcium (iCa²⁺) levels at admission and mortality in trauma patients remains controversial, with prior studies suggesting increased mortality in both hypocalcemic and hypercalcemic states. This study aimed to characterize the relationship between admission iCa²⁺ and key clinical outcomes, including mortality, and to clarify the contribution of acidosis—particularly among patients presenting with elevated iCa²⁺ levels. We performed a retrospective multicenter cohort study using a trauma registry (2011–2021). Adult trauma patients admitted to a level-1 trauma center with measured admission iCa²⁺ were included. Hypocalcemia and hypercalcemia were defined as iCa²⁺ <1.10 mmol/L and > 1.20 mmol/L, respectively. The primary outcome was mortality at hospital discharge (MHD); secondary outcomes were massive transfusion and trauma-induced coagulopathy (TIC). Associations were evaluated using multivariable logistic regression. We additionally assessed whether incorporating pH-adjusted iCa²⁺ improved the predictive performance of the mortality model. Among 977 patients (93% blunt trauma; median ISS 25 [IQR 17–33]), hypocalcemia was observed in 291 (30%) and hypercalcemia in 80 (8%). In multivariable analysis, hypocalcemia was independently associated with MHD (OR 1.70, 95% CI 1.02–2.85) and TIC (OR 2.24, 95% CI 1.58–3.18), but not with massive transfusion. Incorporating pH-adjusted iCa²⁺ did not improve model performance (AUC 0.937, 95% CI 0.920–0.952 vs. 0.940, 95% CI 0.922–0.954 with unadjusted iCa²⁺) for predicting MHD, whereas pH-adjusted hypocalcemia was independently associated with 24-hours mortality (OR 5.35, 95% CI 2.70–10.60), as was pH < 7.3 (OR 3.19, 95% CI 1.64–6.21). Compared with normocalcemic patients, hypercalcemic patients had higher mortality, were not more severely injured, but were more acidotic (pH < 7.3: 33% vs. 16%, p < 0.001) and more frequently had prehospital cardiac arrest (8% vs. 3%, p < 0.001). In severely injured trauma patients, admission hypocalcemia is independently associated with TIC and MHD, underscoring its value as an early indicator of physiological derangement. In contrast, the increased mortality observed in patients with iCa²⁺ >1.20 mmol/L appears largely attributable to profound metabolic acidosis and shock. Recognizing this acidosis-driven elevation in iCa²⁺ may help anticipate the subsequent decline in iCa²⁺ that can occur as pH normalizes during resuscitation.