Final answer:
The order of draw determines when the royal blue tube is drawn in blood collection, designed to prevent cross-contamination and ensure accurate test results.
Step-by-step explanation:
The order in which a royal blue tube is drawn during a blood draw procedure is determined by the blood draw protocol known as the order of draw. The order of draw is crucial because it minimizes the risk of cross-contamination between additives in different tubes which could affect test results. The royal blue tube, which can be used for trace element testing, toxicology, or nutrient determinations, is typically drawn following the light blue tube if coagulation tests are needed since the light blue tube contains an anticoagulant that minimizes the risk of clotting.