Admission ionized hypocalcemia and outcomes in major trauma: a single-center retrospective cohort study comparing two thresholds

Admission ionized hypocalcemia is increasingly recognized as a prognostic marker in major trauma; however, the threshold that best discriminates clinically relevant risk remains uncertain. In particular, whether hypocalcemia defined by the lower reference limit (ionized calcium [iCa] < 1.12 mmol/L) and more severe hypocalcemia (iCa < 1.0 mmol/L) convey distinct prognostic information has not been evaluated within the same cohort. We investigated the associations of admission iCa with mortality and massive transfusion in adult patients with major trauma, comparing these two predefined thresholds. This retrospective cohort study was conducted at a single Level 1 Regional Trauma Center and Regional Emergency Medical Center in the Republic of Korea from January 2016 through December 2023. Adults aged ≥ 18 years with major trauma, defined as an Injury Severity Score ≥ 16, and an available admission iCa measurement were included. The primary outcome was all-cause in-hospital mortality. Secondary outcomes were 4-hour mortality and the requirement for massive transfusion. Multivariable logistic regression was used to estimate adjusted odds ratios for hypocalcemia and severe hypocalcemia. Subgroup analyses were performed according to mode of arrival, categorized as direct transport or interhospital transfer. Among 2,486 patients, 883 (35.5%) had hypocalcemia and 117 (4.7%) had severe hypocalcemia. Overall in-hospital mortality was 18.1%. After adjustment, severe hypocalcemia was independently associated with in-hospital mortality (adjusted odds ratio [aOR], 1.78; 95% confidence interval [CI], 1.07–2.96), whereas hypocalcemia was not (aOR, 1.24; 95% CI, 0.95–1.62). Both hypocalcemia and severe hypocalcemia were associated with massive transfusion (aOR, 1.81; 95% CI, 1.30–2.51; and aOR, 1.94; 95% CI, 1.13–3.25, respectively). Neither threshold was associated with 4-hour mortality. In an exploratory subgroup analysis, the association with mortality was observed among patients transferred from referring hospitals but not among directly transported patients. In adult patients with major trauma, severe admission ionized hypocalcemia, but not hypocalcemia overall, was independently associated with in-hospital mortality. Both thresholds were associated with increased massive transfusion requirements. These findings suggest a severity-dependent prognostic gradient for admission ionized hypocalcemia and indicate that its prognostic significance in major trauma may vary according to the threshold used to define hypocalcemia. Not applicable. Not applicable.