A prospective, observational study has found that the ratio of total-to-ionized calcium independently predicts mortality in critically ill patients with acute kidney injury receiving continuous renal replacement therapy with regional citrate anticoagulation. The researchers found that a ratio of total-to-ionized calcium ≥2.4 was associated with a 33.5-fold increase in 28-day mortality. A significant correlation was also found between total-to-ionized calcium ratio, hepatic clearance and severity of critical illness.