Which test is typically NOT performed with a light blue tube?

The light blue tube is specifically designed for coagulation studies because it contains sodium citrate, which acts as an anticoagulant by binding calcium in the blood sample. This property allows for accurate measurement of clotting factors and time, making it ideal for tests such as Prothrombin Time (PT) and Partial Thromboplastin Time (PTT).

Serum glucose testing, on the other hand, requires the use of serum that is typically collected in a red or gray tube, which does not contain anticoagulants. Since serum glucose testing needs a clear separation of serum from the red blood cells after centrifugation, a light blue tube is not appropriate for this type of analysis. Therefore, serum glucose testing is the correct answer, as it is not performed with a light blue tube.