Mechanism of Action of Calcium Citrate in Preventing Coagulation

Role of Calcium in Coagulation

Calcium ions are essential cofactors in the activation of multiple coagulation factors, including factors II, VII, IX, and X, as well as proteins C and S 1
Calcium enables the binding of coagulation factors to cell membranes and extracellular vesicles, which is a prerequisite for thrombin formation 2, 3
Calcium is necessary for fibrin polymerization and stabilization during clot formation 1
Calcium is required for platelet adhesion at sites of vessel injury 1

Calcium citrate functions as an anticoagulant by chelating ionized calcium in the blood, thereby preventing the calcium-dependent steps in the coagulation cascade 2, 3
Hirudin, which directly inhibits thrombin, is an example of an anticoagulant with a different mechanism of action than calcium citrate 2
Heparin, which indirectly inhibits thrombin by binding to anti-thrombin, is another example of an anticoagulant with a different mechanism of action than calcium citrate 2
Factor Xa inhibitors, which block a specific coagulation factor, also have a different mechanism of action than calcium citrate 1

Excessive citrate load during massive transfusions can lead to hypocalcemia in the recipient due to the chelation of the patient's calcium 4
Hypocalcemia from citrate toxicity is more pronounced in patients with liver dysfunction, hypothermia, or hypoperfusion due to impaired citrate metabolism 4
Ionized calcium levels should be monitored during massive transfusions to prevent complications of hypocalcemia, which include coagulopathy, cardiac dysrhythmias, and cardiovascular dysfunction 4
The anticoagulant effect of citrate is not through inhibition of factor Xa, enhancement of fibrinolysis, or inhibition of platelet aggregation, though hypocalcemia can secondarily affect platelet function 1