Educational exam prep, not medical advice. This page teaches what certification exams test. Follow your facility’s policies, your supervising clinician and the manufacturer’s instructions in practice. If you are a patient with a health question, talk to your clinician or see MedlinePlus.
Tubes in order of draw
| Tube | Additive | Typical use | Inversions |
|---|---|---|---|
| Blood culture bottles / sterile tubes | Broth media | Microbiology | Per manufacturer (bottles) |
| Light blue | Sodium citrate (9:1 blood to additive) | Coagulation (PT/INR, aPTT) | 3-4 |
| Red (plastic) / gold or red-gray (SST) | Clot activator; SST adds separator gel | Chemistry, serology | 5 |
| Green / light green (PST) | Sodium or lithium heparin (PST adds gel) | Chemistry (plasma) | 8-10 |
| Lavender / purple; pink | K2EDTA | Hematology (CBC); pink for blood bank | 8-10 |
| Gray | Sodium fluoride / potassium oxalate | Glucose, lactate | 8-10 |
Why it matters
- EDTA carryover into a chemistry tube falsely raises potassium and lowers calcium - one reason EDTA comes late in the order.
- Underfilled light blue tubes change the 9:1 blood-to-citrate ratio and prolong clotting times.
- Too-vigorous mixing causes hemolysis - invert gently, don’t shake.
- With a winged (butterfly) set, draw a discard tube before a light blue tube if it is the first tube, so the tubing air space does not underfill it.
Practice
Test yourself on the phlebotomy order-of-draw
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Frequently asked questions
What does a lavender top tube contain?
EDTA, used mainly for hematology tests like the CBC.
What is the light blue tube used for?
Coagulation testing; it contains sodium citrate.
How many times do you invert an SST?
Five times per BD guidance.
What is the gray top tube for?
Glucose and lactate - it contains sodium fluoride (a glycolysis inhibitor) and potassium oxalate.
Sources
- BD - Vacutainer Order of Draw and tube guide (accessed 2026-09-23)
- NHA - CPT Test Plan (2024 job analysis) (accessed 2026-09-23)
- CLSI GP41 - Collection of Diagnostic Venous Blood Specimens (standard reference) (accessed 2026-09-23)