Phlebotomy Order of Draw: Tube Colors, Additives and Practice Quiz
Updated October 26, 2026
The order of draw is the sequence for filling blood collection tubes during a venipuncture. Following it keeps the additive in one tube from contaminating the next and changing the test results. It’s one of the most tested topics on the NHA CPT exam. The order below follows the Clinical and Laboratory Standards Institute (CLSI) standard for venipuncture, which the exam is based on.
The order of draw
| Order | Tube | Additive | Common uses |
|---|---|---|---|
| 1 | Blood culture bottles (or yellow SPS tube) | Culture media or SPS | Blood cultures |
| 2 | Light blue | Sodium citrate | Coagulation tests (PT/INR, PTT) |
| 3 | Red, or gold/red-gray (serum separator) | Clot activator, with or without gel | Chemistry, serology |
| 4 | Green | Heparin | Plasma chemistry, ammonia |
| 5 | Lavender or purple | EDTA | Hematology (CBC), HbA1c |
| 6 | Gray | Sodium fluoride and potassium oxalate | Glucose, lactic acid, alcohol |
A memory trick: “Stop Light Red, Stay Put, Green Light Go”: Sterile (cultures), Light blue, Red, SST (serum separator), PST (light green plasma separator, which contains heparin), Green, Lavender, Gray.
Why the order matters
- Blood cultures come first so the sample stays sterile.
- Light blue comes before the serum and additive tubes because carryover of clot activator, heparin or EDTA would throw off coagulation results.
- EDTA comes late because it binds calcium and contains potassium, so carryover can falsely raise potassium and lower calcium in a chemistry tube.
Two details that are often tested
The discard tube. When you use a butterfly (winged) needle and a light blue tube is the first tube drawn, draw a discard tube first, a plain red or another light blue tube, to fill the tubing’s air space. Otherwise the light blue tube is underfilled, and the blood-to-citrate ratio is wrong.
Inversions. Gently invert each tube right after filling, never shake it. The usual counts are 3 to 4 inversions for light blue, 5 for red and serum separator tubes, and 8 to 10 for green, lavender and gray. Check your tube manufacturer’s instructions.
Free order of draw practice questions
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Which tube is drawn first during a routine venipuncture that also includes blood cultures?Answer: BBlood culture bottles always come first, so the sample isn't contaminated by other tubes or additives and stays sterile.
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A physician orders a PT/INR, a CBC and a basic metabolic panel in a serum separator tube. In what order should the tubes be drawn?Answer: CLight blue (citrate, for the PT/INR) comes before the serum separator tube, and lavender (EDTA, for the CBC) comes after both.
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Which additive is in a lavender-top tube?Answer: DLavender (purple) tubes contain EDTA, which prevents clotting by binding calcium. They're used for hematology tests such as a CBC.
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Why is the gray-top tube drawn last?Answer: AThe gray tube's additives, sodium fluoride (which stops glucose breakdown) and potassium oxalate, could interfere with other tests if carried over. Drawing it last avoids that.
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Carryover of EDTA into a chemistry tube is most likely to cause which result?Answer: BEDTA is often a potassium salt, so it can raise potassium, and it binds calcium, so calcium reads low. That's why lavender tubes come after the serum and heparin tubes.
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A light blue tube is the first tube drawn using a butterfly needle. What should the phlebotomist do?Answer: CThe butterfly tubing contains air, which would underfill the first tube. A light blue tube must be filled correctly for the right blood-to-citrate ratio, so draw a discard tube first.
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How should a lavender-top tube be mixed right after it is filled?Answer: DGentle inversion mixes the EDTA with the blood to prevent clotting without damaging the cells. Shaking can cause hemolysis. Lavender, green and gray tubes typically need 8 to 10 inversions.
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