Order of Draw & Blood Tube Colors
The order of draw is the sequence phlebotomists follow when filling blood collection tubes. It exists to stop additives from one tube carrying over into the next (cross-contamination), which would give false results. Below is the CLSI standard order with each tube's stopper color, additive, what it tests, and how many times to invert it — plus an easy mnemonic and the different order used for a fingerstick.
The CLSI order of draw (venipuncture)
| # | Tube (stopper color) | Additive | What it does | Common tests | Inversions |
|---|---|---|---|---|---|
| 1 | Blood culture (sterile) | SPS (sodium polyanethol sulfonate) or culture broth | Drawn first so the sterile site is not contaminated by other tubes' additives | Blood cultures (bacteria/fungi) | 8–10 (gentle) |
| 2 | Light blue | Sodium citrate (3.2%) | Anticoagulant that binds calcium; the 9:1 blood-to-additive ratio must be exact, so the tube is filled completely | Coagulation — PT, PTT/aPTT, INR, D-dimer | 3–4 |
| 3 | Red (plain) / Gold or tiger-top (SST) | None (red) · clot activator + gel separator (gold/SST) | Blood is allowed to clot to give serum; the gel in an SST separates serum from cells after centrifuging | Chemistry, serology, most serum tests | Red 0 · SST 5 |
| 4 | Green | Heparin (lithium or sodium) | Anticoagulant that inhibits thrombin, giving plasma quickly — useful for STAT chemistry | STAT/plasma chemistry, electrolytes, ammonia | 8–10 |
| 5 | Lavender / purple | EDTA (K2/K3) | Anticoagulant that binds calcium and preserves cell shape — drawn after heparin so EDTA (which can raise K+ / lower Ca) does not contaminate other tubes | Hematology — CBC, ESR; blood bank/type & screen | 8–10 |
| 6 | Gray | Sodium fluoride + potassium oxalate | Fluoride is antiglycolytic (stops cells consuming glucose); oxalate anticoagulates — drawn last because oxalate would skew electrolytes if carried over | Glucose, glucose tolerance test, lactate, blood alcohol | 8–10 |
Gently invert additive tubes (never shake — shaking causes hemolysis). A plain red tube has no additive and needs no inversions.
An easy way to remember it
“Boys Like Reading Short Green Lab Guides”
Boys = Blood culture · Like = Light blue · Reading = Red · Short = SST (gold) · Green = Green · Lab = Lavender · Guides = Gray
Additional tubes (less common)
- Royal blue: Trace elements / toxicology (comes with no additive, EDTA, or heparin). Its position in the order follows whichever additive it contains. Less commonly seen.
- Pink: K2EDTA for the blood bank (type & screen, crossmatch). It is an EDTA tube, so it is drawn with the lavender/EDTA group. Less commonly seen.
Capillary (fingerstick) order is different
For a dermal/capillary collection the order is reversed for additives: the EDTA (lavender) tube is collected first so the CBC is accurate before the fast-clotting fingerstick sample causes platelets to clump.
- Blood gas specimen (if collected)
- EDTA (lavender) tube — FIRST among additives, to get an accurate CBC before platelets clump
- Other additive tubes (e.g. heparin)
- Serum tubes — LAST
Frequently asked questions
What is the correct order of draw for a blood collection?
Following the CLSI standard, the venipuncture order of draw is: (1) blood culture / sterile tubes, (2) light-blue sodium citrate (coagulation), (3) red or gold/SST serum tubes, (4) green heparin, (5) lavender/purple EDTA, and (6) gray sodium fluoride. The order prevents additive carryover from one tube contaminating the next.
Why is the light-blue (citrate) tube drawn before the red or serum tube?
The light-blue coagulation tube is drawn early (right after any blood cultures) so it is filled cleanly and accurately at the 9:1 blood-to-citrate ratio. Drawing it after additive tubes risks carryover that would alter delicate clotting results.
Why is the lavender EDTA tube drawn near the end?
EDTA binds calcium and can carry over to raise potassium and lower calcium/other analytes in later tubes, so it is drawn after the serum and heparin tubes and before only the gray tube.
What does the gray-top tube test, and why is it last?
The gray tube contains sodium fluoride (which preserves glucose) and potassium oxalate (an anticoagulant). It is drawn last because oxalate carryover would distort electrolyte and coagulation results in other tubes. It is used for glucose, glucose tolerance testing, lactate, and blood alcohol.
Why are blood cultures always collected first?
Blood cultures are collected first, using strict aseptic technique, so the sterile specimen is not contaminated by microorganisms or additives carried over from other tubes — contamination could cause a false-positive culture.
Is the order of draw different for a fingerstick (capillary) collection?
Yes. In a capillary/dermal collection the EDTA (lavender) tube is collected FIRST, then other additive tubes, then serum tubes last. Because a fingerstick clots quickly and platelets clump, hematology (CBC) must be collected first to stay accurate — the reverse of venipuncture.
How many times should each tube be inverted?
Gently invert (do not shake) per the manufacturer: light-blue citrate 3–4 times, gold/SST about 5 times, green heparin 8–10 times, lavender EDTA 8–10 times, and gray 8–10 times. A plain red (no-additive) tube needs no inversions. Shaking causes hemolysis.
What happens if the order of draw is wrong?
Drawing tubes out of order lets an additive carry over on the needle into the next tube (additive cross-contamination), which can produce falsely altered results — for example EDTA carryover raising potassium. Wrong order can lead to specimen rejection and repeat draws.
Ready to practice?
Test yourself on the order of draw, tube additives, and the rest of the NHA CPT exam — free, with answer explanations.
Start free phlebotomy practice →Source: CLSI GP41 standard order of draw and common tube-additive references. This guide is for study; always follow your employer's and manufacturer's current procedures.