EDTA and sodium citrate prevent blood coagulation by:

The correct choice refers to the mechanism by which both EDTA (ethylenediaminetetraacetic acid) and sodium citrate function as anticoagulants. These substances work by chelating calcium ions in the blood. Calcium is a crucial component in the coagulation cascade, as it is necessary for several steps in the clotting process, including the activation of certain clotting factors.

By binding to calcium ions, EDTA and sodium citrate effectively inhibit the coagulation cascade, preventing the formation of clots. This chelation of calcium changes the ionic environment and disrupts the biochemical pathways that lead to thrombus creation, making these agents effective in laboratory settings and during certain medical procedures where blood must remain in a fluid state.

While anticoagulants such as antithrombin III have roles in inhibiting thrombin and other factors of the coagulation system, EDTA and sodium citrate do not directly interact with them in this manner. Likewise, the neutralization of thrombin or binding fibrinogen is not the primary mechanism of action for these anticoagulants. Therefore, the ability of EDTA and sodium citrate to chelate calcium is indeed central to their function as effective blood anticoagulants.