Immobilization and prolonged bed rest are harmful to the skeleton, which suffers increased resorption, and contribute to reducing survival rates among patients in critical care units. We report a patient who presented hypercalcemia 10 days after continuous venovenous hemofiltration has ended. Investigative tests showed an increase of serum C-terminal telopeptide of type I collagen (CTx), with suppressed parathormone and calcitriol. Denosumab was administered with a significant response, decreasing ionized calcium and CTx levels. The calcium infusion rate during dialysis procedures, used for citrate anticoagulation compensation, has progressively decreased, suggesting that endogenous calcium was taking part in the citrate chelation. In this report, we highlight the challenges in early diagnosis of immobilization-induced hypercalcemia among patients who are on continuous renal replacement therapy undergoing citrate anticoagulation.