Effect of Prothrombin Complex Concentrate versus Frozen Plasma on Divalent Cations and Vitamin K Dependent Factor...

Prothrombin complex concentrate (PCC) has demonstrated hemostatic superiority over frozen plasma (FP) in cardiac surgery, yet the mechanism beyond factor concentration remains unclear.

To test ex vivo whether citrate-mediated depletion of ionized calcium (Ca²⁺) and magnesium (Mg²⁺) by FP impairs vitamin K dependent (VKD) factor function, minimized by PCC.

Heparinized whole blood from healthy volunteers (n=10) was diluted and supplemented with 20% FP or volume-equivalent PCC. Coagulation was assessed by heparinase-modified INTEM (ROTEM) and contact-activated thrombin generation, and validated in cardiopulmonary bypass (CPB) samples (n=6). Factor IX (FIX) and Factor X γ-carboxyglutamate (Gla) domain affinities for Ca²⁺ and Mg²⁺ were measured by MicroScale Thermophoresis (MST).

FP reduced Ca²⁺ from 0.94 ± 0.03 to 0.24 ± 0.01 mmol·L^-1 and Mg²⁺ to undetectable levels. Without exogenous calcium, FP abolished clot formation (clotting time, CT >3600 s) whereas PCC maintained CT (105.4 ± 16.9 s). Low-dose calcium (0.4 mmol·L^-1) partially restored CT (1037 ± 575.5 s); adding MgSO₄ (0.6 mmol·L^-1) improved it to 275.2 ± 56.2 s. Findings held in CPB samples. By MST, the FIX Gla domain bound Mg²⁺ ∼6-fold more tightly than Ca²⁺ (Kd 66.1 ± 8.2 vs 381.2 ± 45.3 μM).

Lowering ionized calcium with FP-derived citrate revealed a functional interaction between magnesium and the Gla domain of VKD factors: at low calcium, restoring magnesium rather than calcium alone recovered thrombin generation and clot formation. PCC preserved the ionic milieu and thrombin generation. Standard coagulation assays potentially underestimate this magnesium dependence because of supraphysiological recalcification.