Thrombin or CaCl2 are typically used for what purpose?

Thrombin and CaCl2 (calcium chloride) are agents commonly used in laboratory settings to initiate the clotting process in anti-coagulated plasma. When blood is drawn into a tube containing anticoagulants, such as EDTA or citrate, it does not clot naturally due to the presence of these anticoagulants. To study clotting mechanisms or for various downstream applications, it becomes necessary to induce clotting to obtain serum or to analyze the clotting factors. Thrombin acts as a proteolytic enzyme that converts fibrinogen to fibrin, facilitating the formation of a clot, while CaCl2 provides the necessary calcium ions that help in the clotting cascade. This makes the first answer a clear choice for the purpose of thrombin and CaCl2 in laboratory contexts.