Predictive accuracy of serum total calcium for both critically high and critically low ionized calcium in critical illness

Background Methods The accuracy of total calcium and its corrected value for predicting critically high and critically low ionized calcium in critical illness is controversial. The aim of this study was to investigate whether the concentration of total serum calcium, either corrected for albumin or not, could predict critically high or low values in critical illness. This report describes a retrospective study using the Medical Information Mart for Intensive Care (MIMIC) III database. Test panels that contained serum albumin, total calcium, and ionized calcium (named ATI panels) with order time intervals of less than one hour were extracted. The predictive accuracy of total calcium, either corrected for albumin or not, was assessed using receiver operating characteristic (ROC) curve analysis. Results Conclusions A total of 12 118 ATIs with 103 critically low and 92 critically high ionized calcium results were extracted. The areas under ROC curves (AUCs) of corrected and uncorrected total calcium for predicting critically low ionized calcium were 0.69 (95% CI: 0.61-0.76) and 0.70 (95% CI: 0.63-0.78), respectively. For predicting critically high ionized calcium, the AUCs were 0.98 (95% CI: 0.97-1.00) and 0.97 (95% CI: 0.95-1.00), respectively. With positive predictive values (PPVs) of 0.05 and 0.10, the sensitivities (both corrected and uncorrected) were approximately 0.50 for predicting critically low ionized calcium and 0.95 for predicting critically high ionized calcium. Total calcium, either corrected for albumin or not, is not a reliable test to predict critically low ionized calcium in critical illness. Total calcium's predictive accuracy for critically high ionized calcium is high.