What is the primary use of a light blue top tube in phlebotomy?

The light blue top tube is primarily used for coagulation studies, which is why this option is the correct choice. This tube contains sodium citrate as an anticoagulant, which works by binding calcium in the blood, thereby preventing clot formation. This is essential for accurate results when measuring clotting parameters such as prothrombin time (PT) and partial thromboplastin time (PTT).

In contrast, the other tube colors are designed for different purposes; for instance, tubes with red tops are typically used for blood chemistry tests that require serum, while green tops may contain heparin for specific plasma chemistry tests. The light blue top tube’s unique composition is tailored specifically for tests that evaluate the coagulation system, making it crucial for accurate assessments in patients needing coagulation monitoring.