Blood samples must be drawn by phlebotomists in a specific order. This is important to avoid cross-contamination of the sample by additives found in different collection tubes. Cross contamination can occur when blood in an additive tube comes in contact with a needle and when blood is transferred from a syringe into tubes.

Filling tubes in wrong order will cause interference in specimen testing from cross contamination, tissue thromboplastin and microorganisms.

This order of draw applies for all specimens collected by syringe, tube holder, or into pre evacuated tubes.