The standard order of draw for venipuncture, set by the Clinical and Laboratory Standards Institute (CLSI), follows this sequence: blood culture bottles first, then light blue, red/gold, green, lavender/pink, and gray tubes last. This specific sequence prevents chemical additives in one tube from contaminating the next and skewing test results.
The Standard Order of Draw
Here is the complete sequence, listed by tube color and what each tube contains:
- Blood culture bottles (yellow/black tops): Collected first to maintain sterility. A set typically includes one aerobic and one anaerobic bottle, each filled with 10 mL of blood for a total of 20 mL per set.
- Light blue top: Contains 3.2% sodium citrate, an anticoagulant used for coagulation studies like PT and PTT.
- Red top (plain) and gold/tiger top (SST): Red tops have no additive at all. Gold tops, also called serum separator tubes, contain a clot activator and a gel barrier that separates serum from the clot during centrifugation. Both are used for serum-based chemistry and immunology tests.
- Green top (dark green, light green, or speckled green): Contains heparin, either lithium heparin or sodium heparin, which prevents clotting. Light green tubes also include a gel separator for plasma testing.
- Lavender (purple) top, pink top, and pearl top: All contain EDTA, an anticoagulant that preserves blood cells. Lavender is the standard for complete blood counts. Pink tubes use the same additive but are designated for blood bank testing. Pearl tops add a gel separator for plasma preparation.
- Gray top: Contains sodium fluoride and potassium oxalate. The sodium fluoride inhibits glycolysis, which means it stops blood cells from continuing to consume glucose after the sample is drawn. This makes it the go-to tube for accurate glucose and lactate measurements.
A useful mnemonic some phlebotomists learn: “Boys Love Red Gold Greens, Love Playing Guitar” (blood culture, light blue, red, gold, green, lavender, pink, gray).
Why the Sequence Matters
When you puncture a vacuum tube with a needle, a tiny amount of additive can cling to the needle’s interior and transfer into the next tube. This is called additive carryover, and it can produce clinically significant errors in test results.
EDTA is the most problematic additive if it contaminates other tubes. It binds calcium, which is essential for blood clotting. If EDTA carries over into a light blue (citrate) tube, it artificially prolongs clotting times and can lead to a misdiagnosis of a bleeding disorder. If it reaches a green or red tube, it can falsely lower calcium levels on a metabolic panel. The order of draw places EDTA tubes near the end specifically to keep this additive away from chemistry and coagulation samples.
Blood cultures sit at position one for a different reason: sterility. Any tube drawn before the culture bottles could introduce skin bacteria or contaminants from previous tube stoppers into the culture medium, producing a false positive that might lead to unnecessary antibiotic treatment.
Special Rules for Light Blue Tubes
Light blue tubes are the most finicky in the sequence. The ratio of blood to sodium citrate must be exactly 9 parts blood to 1 part anticoagulant. CLSI guidelines allow a tolerance of plus or minus 10% of the tube’s stated draw volume, but anything outside that range can distort coagulation results. An underfilled tube has too much citrate relative to blood, which artificially prolongs clotting times. An overfilled tube has too little citrate, which can cause partial clotting in the sample.
Most tubes have a minimum fill line printed on the label. If the blood level falls below that mark, the sample should be redrawn rather than sent to the lab.
Red Top vs. Gold Top
These two tubes occupy the same position in the order of draw, but they are not interchangeable. Gold SST tubes contain a clot activator that speeds up the clotting process plus a gel barrier that physically separates serum from cells after centrifugation. They’re the standard for routine chemistry panels: basic metabolic panel, comprehensive metabolic panel, lipid panel, and liver function tests.
Plain red tops contain nothing at all. Blood simply clots naturally inside the tube. These are reserved for specific tests where the gel barrier could interfere with results, particularly certain drug levels (since some medications bind to the gel) and specialized immunohematology testing. If a lab order calls for a red top, substituting a gold SST can produce inaccurate results.
Mixing After Collection
Every tube with an additive needs to be gently inverted 6 to 8 times immediately after filling. This ensures the blood mixes thoroughly with the anticoagulant or preservative. Shaking is not the same as inverting. Vigorous shaking can damage red blood cells (hemolysis), which ruins the sample and often requires a redraw. A smooth, end-over-end rotation is all that’s needed.
Plain red tops with no additive don’t require mixing, but they do need to sit undisturbed for 30 to 60 minutes to allow complete clotting before centrifugation.
Capillary (Fingerstick) Order of Draw
The order changes for skin puncture collections like fingersticks and heelsticks. Because capillary samples are small and blood flow is limited, the priority shifts to filling the most volume-sensitive tubes first:
- Blood gas capillary tubes
- EDTA microcollection tubes
- Other additive tubes (heparin, sodium fluoride)
- Serum microcollection tubes
EDTA moves to near the top of the capillary sequence because platelet clumping begins almost immediately at a skin puncture site. If the EDTA tube is filled last, the sample may already contain tiny clots that make a complete blood count inaccurate. Serum tubes go last because clotting is actually desirable in those samples, so partial clotting during collection is less of a concern.
Less Common Tube Colors
A few tubes don’t appear in every standard draw but have specific positions when they’re ordered. Royal blue tops come in two versions: one with EDTA and one with no additive. They’re made from specially purified glass and stoppers to avoid trace metal contamination, so they’re used for tests like zinc, lead, and other heavy metals. Their position in the draw depends on which version is used: the EDTA version draws with other EDTA tubes, while the plain version draws with serum tubes.
Yellow tops containing ACD (a solution of citrate, citric acid, and dextrose) are used for specialized tests like HLA typing and some blood bank procedures. Different facilities place them at slightly different points in the sequence, so checking your lab’s specific protocol is worthwhile when these tubes come up.