What type of vacutainer (vacuum blood collection tube) is used for serum electrolyte testing?

Serum Electrolytes Testing: Vacutainer Selection

Serum electrolytes samples should be collected in serum separator tubes (SST), which are typically gold/yellow-topped or tiger-topped tubes containing clot activators and gel separators. 1

Characteristics of Serum Collection Tubes for Electrolytes

• Plain red top tubes (glass with no additive or plastic coated with silica as clot activator) or serum separator tubes (SST; gold top or tiger top) with clot activators and gel separators are commonly used for serum collection for electrolyte testing 1
• Serum separator tubes contain clot activators that accelerate the clotting process and gel separators that form a barrier between serum and blood cells after centrifugation 1
• The gel separator in SST tubes prevents contamination of serum with cellular components, which can affect electrolyte measurements 1

Proper Collection Procedure

• Follow the recommended blood draw order to avoid cross-contamination when collecting multiple samples:

  1. Blood culture tube or bottle
  2. Sodium citrate tube
  3. Serum tube (for electrolytes)
  4. Heparin tube
  5. EDTA tube
  6. Sodium fluoride/potassium oxalate glycolytic inhibitor tube 1

• Proper clotting time is essential for accurate electrolyte measurements:

  • BD Diagnostic recommends a 30-minute clotting time for SST tubes 1
  • Plain red top tubes require a 60-minute clotting time 1
  • Blood samples should be left upright at room temperature for at least 30 minutes but no more than 60 minutes to allow clots to form 1

Processing Considerations

• After collection, gently invert the tube according to manufacturer's recommendations to ensure proper mixing of the clot activator with the blood 1
• Insufficient clotting may lead to formation of residual fibrin, which can clog analyzing instruments 1
• Prolonged clotting may lead to cell lysis, resulting in serum contamination with cellular components that can affect electrolyte values 1
• Pre-centrifugation delay should be minimized; ideally complete processing within 2 hours 1

Advantages of Serum for Electrolyte Testing

• Serum specimens remain stable after centrifugation and show more accurate results than plasma for many analytes 2
• Serum is the most convenient sample type for routine laboratory analysis, including electrolytes 3
• Serum does not contain anticoagulants that might interfere with certain electrolyte measurements, particularly potassium 1, 4

Special Considerations

• Patients with certain diseases (liver diseases, multiple myeloma) or those on anticoagulant therapy may require longer clotting times 1
• Quick-clotting serum separator tubes (e.g., VQ-Tube™) are available for faster turnaround times while maintaining accuracy for most electrolyte measurements 2
• Potassium levels may show clinically significant differences between serum and plasma samples (typically higher in serum) 4