Calcium level is associated with sudden cardiac death based on several cohort studies. However, there is limited evidence on the association between ionized calcium, active form of calcium, and resuscitation outcome. This study aimed to evaluate the potential role of ionized calcium in predicting resuscitation outcome in patients with out-of-hospital cardiac arrest. We analyzed the Korean Cardiac Arrest Research Consortium data (KoCARC) registry, a web-based multicenter registry that included

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... participating hospitals throughout the Republic of Korea. The patients with out-of-hospital cardiac arrest over 19 years old and acquired laboratory data including calcium, ionized calcium, potassium, phosphorus, creatinine, albumin at emergency department (ED) arrival were included. The primary outcome was successful rate of return of spontaneous circulation (ROSC) and the secondary outcomes were survival hospital discharge and favorable neurological outcome (cerebral performance category 1 or 2) at hospital discharge. Eight-hundred and eighty-three patients were enrolled in the final analysis and 448 cases (54%) had ROSC. In multivariable logistic regression analysis, ionized calcium level was associated with ROSC (odds ratio, 1.77; 95% CI1.28-2.45; p = 0.001) even though calcium level was not associated with ROSC (odds ratio, 0.87; 95% CI 0.70-1.08; p = 0.199). However, ionized calcium level was not associated with survival discharge (odds ratio, 0.99; 95% CI 0.72-1.36; p = 0.948) or favorable neurologic outcome (odds ratio, 0.45; 95% CI 0.03-6.55, p = 0.560). A high ionized calcium level measured during cardiopulmonary resuscitation was associated with an increased likelihood of ROSC.