Which substance in PRBCs can chelate calcium and affect coagulation?

Citrate is the correct answer because it is commonly used as an anticoagulant in the storage of packed red blood cells (PRBCs). Citrate binds to calcium ions in the blood, effectively reducing the availability of calcium needed for many essential steps in the coagulation cascade. Calcium plays a critical role in the coagulation process, particularly in the activation of several clotting factors, and its depletion can lead to a decreased ability to form clots.

Citrate, therefore, serves an important purpose in blood banking by preventing clotting during the collection and storage of blood products. When PRBCs are transfused, the citrate can continue to affect the recipient’s coagulation status if the transfusion volume is significant, which is something that clinicians need to be aware of, especially in massive transfusion protocols.

The other substances mentioned in the options do not play a role in chelating calcium in the same way. Vitamin K is essential for the synthesis of certain clotting factors but does not chelate calcium. Fibrinogen is a key protein in the coagulation process, necessary for clot formation, and does not interact with calcium ions in the manner that citrate does. Additionally, while calcium itself is essential for coagulation, it is