MLT GlobeOrder of Draw & Tube Colours
Collect tubes in this order to avoid additive carry-over between tubes.
| Tube | Additive | Used for |
|---|---|---|
| 1. Light blue | Buffered sodium citrate, 3.2% (0.109 mol/L) | Coagulation tests such as PT/INR, aPTT, fibrinogen, D-dimer and factor assays |
| 2. Red | Plastic tube with silica clot activator and no gel (glass red tubes contain no additive) | Serum chemistry, serology and immunology, therapeutic drug levels and blood bank tests where a gel-free serum is required |
| 3. Gold, or red/gray mottled ('tiger') top (serum separator tube, SST) | Silica clot activator with a polymer separator gel | Routine serum chemistry, immunoassays (e.g. hormones, tumor markers) and infectious disease serology |
| 4. Green | Sodium heparin or lithium heparin, no gel | Plasma chemistry, ammonia and specialized tests needing whole blood or plasma; do not use sodium heparin for sodium or lithium heparin for lithium levels |
| 5. Light green, or green/gray mottled top (plasma separator tube, PST) | Lithium heparin with a polymer separator gel | Routine and urgent (STAT) plasma chemistry such as electrolytes, renal and liver function and cardiac markers |
| 6. Lavender/purple (pink for blood bank) | Spray-dried dipotassium EDTA (K2EDTA) | Hematology (CBC, ESR, blood smears), HbA1c, blood grouping and crossmatch (pink tube) and many molecular tests |
| 7. Gray | Sodium fluoride with potassium oxalate (or with Na2EDTA) | Glucose, especially when testing is delayed, lactate (transport on ice) and blood alcohol |
Light blue
Citrate binds calcium so the clotting cascade cannot proceed; the tube must be filled to the line to keep the 9:1 blood-to-citrate ratio.
Red
Silica particles speed up clotting so serum can be separated after centrifugation; with no gel, serum must be transferred off the cells promptly.
Gold, or red/gray mottled ('tiger') top (serum separator tube, SST)
The activator speeds clotting, and on centrifugation the gel moves to form a barrier between serum and the clot.
Green
Heparin boosts antithrombin, which inactivates thrombin and factor Xa, so blood stays unclotted and plasma is obtained.
Light green, or green/gray mottled top (plasma separator tube, PST)
Heparin, via antithrombin, stops thrombin and factor Xa from working; the gel separates plasma from cells after centrifugation.
Lavender/purple (pink for blood bank)
EDTA chelates calcium, preventing clotting while preserving blood cell shape and size.
Gray
Fluoride blocks the glycolytic enzyme enolase so cells stop consuming glucose; oxalate or EDTA prevents clotting by removing calcium.
Always follow your own laboratory's collection procedure.