What role does Sodium Citrate serve in laboratory testing?

Sodium Citrate primarily serves as an anticoagulant in laboratory testing, specifically in blue top tubes. It works by binding calcium ions in the blood, which are essential for the coagulation cascade; by doing so, it prevents blood from clotting. This allows for accurate determination of coagulation factors, making sodium citrate particularly important in tests such as prothrombin time (PT) and activated partial thromboplastin time (aPTT), which evaluate the blood's ability to clot properly.

While other options mention different functions related to laboratory testing, sodium citrate is distinctively recognized for its role in blue top tubes used for coagulation studies. Lavender top tubes, for example, usually contain EDTA as the anticoagulant, and preservatives for urine samples are typically other substances like boric acid. Culture media are designed specifically for promoting bacterial growth, which does not relate to the anticoagulation properties of sodium citrate.