What is the primary function of sodium citrate in light blue tubes?

Sodium citrate serves a critical role as an anticoagulant in light blue tubes, which are primarily used for coagulation tests. Its primary function is to prevent clotting by chelating calcium ions in the blood sample. Calcium is a crucial component in the coagulation cascade, and by binding to it, sodium citrate effectively inhibits the various stages of coagulation, allowing for accurate measurement of clotting factors and the overall functionality of the coagulation system. This property is essential in procedures such as prothrombin time (PT) and activated partial thromboplastin time (aPTT) testing, where the understanding of coagulation responses is vital for diagnosis and treatment.