Blood collection tubes must be filled in a specific order to avoid specimen contamination from the additive in the preceding tube. The following order of draw is an accepted laboratory standard.
1. Tubes or bottles for blood cultures
2. Light-blue top tubes (sodium citrate)
3. Serum tubes (with or without clot activator)
4. Green top tubes (sodium or lithium heparin)
5. Lavender or pink top tubes (Potassium EDTA)
6. Gray (Sodium fluoride and sodium or potassium oxalate)