Gold Top Tube / SST
Clot activator + thixotropic gel
The gold top, also called SST (serum separator tube) or "tiger top" when the cap has red and gold bands, is the workhorse of clinical chemistry. Clot activator plus a thixotropic gel that forms a barrier between cells and serum after centrifugation. One spin and the analyzer can sample directly.
The additive.
Two components: a silica clot activator (similar to plastic red) and a thixotropic separator gel. The activator speeds clot formation; the gel sits at the bottom of the tube as a viscous mass and migrates to the cell-serum interface during centrifugation, forming a physical barrier.
The gel barrier is the SST advantage. Once spun, serum can sit in contact with the gel for hours without re-mixing back into the cells. The lab can pipette directly off the top.
The downside: the gel can interact with certain drugs (especially lipophilic ones) and absorb them out of the serum over time. For therapeutic drug monitoring of specific drugs, lab protocols may require plain red instead.
What the gold top is used for.
Comprehensive metabolic panel (CMP), basic metabolic panel (BMP), lipid panel. The chemistry workhorses. Hormones (TSH, cortisol, testosterone), thyroid panels, liver function tests, kidney function tests.
Most routine drug levels (excluding the few drugs that bind the gel). Therapeutic drug monitoring for common medications uses gold.
Most send-out tests when serum is needed and timing flexibility matters. The gel barrier means a sample can ship overnight without re-mixing with cells.
How to draw it correctly.
Draw 3.5 to 8.5 mL. SSTs come in multiple sizes; pick what your test menu needs.
Invert 5 times. The clot activator is silica and needs to mix into the blood; under-mixing leaves silica clumps and incomplete clotting.
Let the tube sit upright for 30 minutes before centrifugation. The clot needs to form completely before you spin. Spinning early means the gel barrier never forms cleanly and serum can re-contact cells.
Three mistakes that cost you a recollect.
- 1
Spinning too early
Clot incomplete. Gel barrier does not form. Serum re-mixes with cells, potassium leaks out of cells over time, result is a falsely-elevated potassium.
- 2
Using gold when blood bank wants red
Gel can interfere with antigen-antibody reactions. Crossmatch may give incorrect results. Always check the test requirement before defaulting to SST.
- 3
Refrigerating before spinning
The gel becomes more viscous when cold and may not migrate properly during centrifugation. Spin at room temperature.
Gold in the order of draw.
Gold (SST) and red are both serum tubes and share CLSI position 3. Either order within the group is acceptable per CLSI. Many labs standardize "red before gold" so the silica clot activator in the SST never has the chance to migrate backward into the plain red.
See the full CLSI order-of-draw page →Common questions about the gold top.
What is the gold top tube used for?
Is the SST the same as the gold top?
How long do I wait before spinning an SST?
Can I use SST for blood bank?
Why does my lab reject SSTs that sat in the fridge?
Six more tubes you will see on the same tray.
- Lavender Lavender/ PurpleCLSI 5 · EDTA (K2 or K3)
- Light Blue Light BlueCLSI 2 · Sodium citrate 3.2%
- Red RedCLSI 3 · None (glass) or clot activator (plastic)
- Green GreenCLSI 4 · Lithium or sodium heparin (PST has gel)
- Gray GrayCLSI 6 · Sodium fluoride + potassium oxalate
- Royal Blue Royal BlueCLSI varies · Trace-element-free (EDTA or no additive)