Calcium ion (Factor IV) (Ca2+)

Calcium ions, historically designated as Factor IV, are essential inorganic cofactors required at multiple stages of the blood coagulation cascade. They facilitate the assembly of multi-component enzyme complexes, such as the tenase and prothrombinase complexes, on the surface of activated platelets and endothelial cells. Specifically, calcium ions form bridges between the gamma-carboxyglutamic acid (Gla) residues of vitamin K-dependent clotting factors (II, VII, IX, and X) and the negatively charged phospholipids of the cell membrane. Without sufficient ionized calcium, these complexes cannot form, effectively halting the production of thrombin and the subsequent formation of a fibrin clot. In medical therapeutics, calcium is primarily targeted through chelation by agents like sodium citrate or EDTA to prevent blood from clotting during storage, transfusion, or extracorporeal circulation. Monitoring ionized calcium levels is critical in clinical settings, particularly during massive transfusions, to avoid citrate-induced hypocalcemia and associated cardiac complications.

Other names

Factor IVDivalent calcium cationCoagulation factor IVCa2+

Chelation of free ionized calcium to prevent the assembly of phospholipid-dependent coagulation complexes.