What is the purpose of drawing blood into a light blue tube before other tubes?

Drawing blood into a light blue tube first serves primarily to prevent contamination from additives used in other tubes. The light blue tube typically contains sodium citrate, which is an anticoagulant that is essential for specific coagulation tests. By collecting this sample first, you ensure that the integrity of the coagulation tests is maintained, as additives from subsequent tubes could interfere with the results.

Using the light blue top tube first minimizes the risk of carryover contamination from tubes that contain different types of additives, such as gel separators or additional anticoagulants. This is particularly important because even small traces of these additives can compromise test accuracy. Therefore, collecting the light blue tube first is a critical step in phlebotomy techniques aimed at ensuring reliable laboratory results.