Final answer:
The first tubes drawn in a standard order of draw are sterile tubes, designed to prevent contamination and preserve sample integrity in blood collection for medical tests.
Step-by-step explanation:
The tubes that are always drawn first in a standard order of draw are sterile tubes. This is to prevent contamination and ensure the integrity of the blood samples. The order of draw is critical in phlebotomy to prevent cross-contamination of additives between tubes. While different institutions may slightly vary their order based on specific needs or tests, the general trend in the standard order of draw follows this sequence: blood cultures (sterile), tubes with clot activators (usually with gel for serum separator tubes), then tubes with anticoagulants. Examples of anticoagulant tubes include heparin tubes, sodium citrate tubes, and EDTA tubes, listed typically in the order of their draw following the sterile tubes.