Anticoagulants are a group of pharmaceuticals that prevent the coagulation or clotting of blood. Anticoagulants are used to prevent clogging of laboratory instruments, blood transfusion bags, and medical equipment. In addition, they are used as additives in blood collection tubes. Commonly used anticoagulants are EDTA, sodium citrate, and heparin. Most anticoagulants (except for heparin), prevent blood clotting by binding Calcium ions, which in turn blocks the activity of coagulation proteins.