Order of Blood Tube Collection: Gold SST Before Lavender EDTA
Fill the gold-top serum separator tube (SST) before the lavender EDTA tube to prevent cross-contamination of EDTA anticoagulant into serum specimens, which can falsely alter critical electrolyte results.
The Standard Order of Draw
The recommended sequence for blood collection follows a specific protocol designed to minimize additive carryover between tubes 1:
- Blood culture tubes (if needed)
- Citrated coagulation tubes (light blue top)
- Serum tubes (red, gold, or tiger tops/SST) ← Draw FIRST between your two options
- Heparin tubes (green tops)
- EDTA tubes (lavender tops) ← Draw SECOND between your two options
- PAXgene or Tempus tubes (for RNA/miRNA)
Why This Order Matters
Risk of EDTA Contamination
When you draw the lavender EDTA tube first, residual EDTA can contaminate subsequent tubes through:
- Needle carryover in closed vacuum systems
- Backflow during collection
- Transfer contamination in syringe collection methods
Clinical Impact of EDTA Carryover
Even small amounts of EDTA contamination significantly alter test results 2:
- Magnesium, calcium, and potassium are altered by K3EDTA whole-blood contamination
- Iron values change at EDTA concentrations of 4.4 mmol/L
- Contamination with just 1 μL of pure K3EDTA solution can affect results
- An absolute volume larger than 10 μL of EDTA whole blood is necessary to alter most test results
Key Practical Points
The Evidence on Carryover Risk
Research demonstrates that EDTA carryover in closed vacuum systems is "highly unlikely" when following proper technique 2. However, the consequences of contamination—particularly for electrolytes like calcium, magnesium, and potassium—are clinically significant enough to warrant strict adherence to the order of draw.
Common Pitfalls to Avoid
- Never reverse the order even when you think you're being careful—the risk isn't worth it
- Discard the first 1-2 mL when drawing from an IV line to clear any contaminants from tubing
- Document your collection method as variations in venous access can affect results 1
- With syringe collection, slight EDTA carryover can occur even without biomarker alteration 2
Tube Performance Considerations
The gold SST demonstrates 3:
- High correlation and comparable stability to standard serum tubes
- Suitable for rapid testing as an alternative
- Clinically comparable differences across most analytes
The lavender EDTA tube is versatile for downstream analyses 1:
- Suitable for genomics, proteomics, and metabolomics
- Less likely to interfere with analyte detection compared to other anticoagulants
- Can be processed to yield plasma, RBCs, and buffy coat components
Bottom Line Algorithm
Always follow this sequence:
- Draw gold SST first
- Draw lavender EDTA second
- If using IV access, discard first 1-2 mL before filling any tubes
- Use closed vacuum system when possible to minimize contamination risk