Massive Transfusion Increases Serum Magnesium Concentration.

(1) Background: The massive transfusion of packed red blood cells (RBCs) is a lifesaving procedure, but it is associated with complications, e.g., dysmagnesemia. Since magnesium is an intracellular ion, the transfused RBCs can significantly influence the magnesium concentration in the recipient's blood. (2) Methods: A retrospective study was performed among 49 patients hospitalized in the Central Clinical Hospital of the Medical University of Warsaw who received a massive blood transfusion (≥4 units/h). Data on laboratory results and patient history were collected from the hospital database. The intracellular RBCs magnesium concentration was measured in 231 samples using the colorimetric method. (3) Results: There were statistically significant changes in the mean serum magnesium concentration preoperatively and 24 h postoperatively (0.87 ± 0.13 vs. 1.03 ± 0.14, < 0.00001) and 48 h postoperatively (0.87 ± 0.13 vs. 1.06 ± 0.15, < 0.00001). Patients who died had significantly higher serum magnesium concentrations ( < 0.05). The median intracellular magnesium concentration in RBCs was 0.91 (0.55-1.8) mmol/L, which is below the reference values of 1.65-2.65 mmol/L. (4) Conclusions: Transfused RBCs significantly increased the serum magnesium concentration 24 h and 48 h postoperatively. It could be a result of mild hemolysis, as the median intracellular magnesium concentration in RBCs was below the reference values.