The standard tube sequence with colors, additives, and the reason the order exists, written in plain words.
Blood cultures · culture bottles, or a yellow tube with SPS Aerobic and anaerobic bottles · sodium polyanethol sulfonate
TestsBlood cultures, looking for bacteria or fungi in the bloodstream.
First, always. Everything after this point involves pushing a needle through rubber stoppers that are not sterile, and anything picked up along the way can grow in a culture bottle and read as an infection the patient does not have.
Light blue · sodium citrate, 3.2 percent Coagulation tube · must be filled to the line
TestsPT and INR, aPTT, fibrinogen, D-dimer, individual factor assays.
This is the one people get wrong. It has to come before any tube containing clot activator. Activator riding over on the needle starts the clotting process early, so a PT or aPTT comes back faster than the patient's blood really is, and a warfarin dose gets adjusted on a number that was never true. The tube also has to reach its fill line, because the amount of citrate in it is measured against a full tube of blood.
Red · no anticoagulant, plain or with clot activator Serum tube · blood is allowed to clot, then spun
TestsGeneral chemistry, serology and antibody titers, drug levels, and blood bank work at some facilities.
Serum tubes sit here because their clot activator is exactly what the citrate tube above cannot tolerate, and because nothing in them harms the tubes that follow.
Gold or speckled · clot activator plus a gel separator SST · the gel forms a barrier between serum and cells
TestsChemistry panels, liver and kidney function, lipids, thyroid studies, most send-out chemistry.
Charts that show six steps instead of seven fold this in with the red tube, since both are serum tubes and the order between them does not change any result. Splitting them out is just easier to read at the bedside.
Green · heparin, lithium or sodium Dark green plain · light green or speckled has gel (PST)
TestsFast turnaround chemistry, ammonia, lactate, ionized calcium, chromosome studies.
Heparin goes ahead of the purple tube because the additive in the purple tube is far more destructive to a chemistry result than heparin is to anything downstream.
Lavender · EDTA Pink and pearl tubes also contain EDTA · pink is common for type and screen
TestsCBC with differential, ESR, hemoglobin A1c, blood type and screen, crossmatch.
EDTA is the biggest troublemaker in the set. It locks up calcium so tightly that a trace of it in the next tube drops the calcium result, and because the additive is a potassium salt, that same trace pushes the potassium result up. A clinician can end up treating a high potassium that only exists on the printout. That is why it sits near the end.
Gray · sodium fluoride with potassium oxalate Glycolytic inhibitor · stops the cells from eating the glucose
TestsGlucose when the sample will sit before testing, lactate, blood alcohol.
Last, because it carries both a sodium salt and a potassium salt and it deliberately shuts down enzyme activity. Anything it contaminates comes back wrong in several directions at once, so nothing is allowed to follow it.
One needle fills every tube in a single draw. Each time that needle punctures a stopper and then leaves it, a film of whatever was in that tube can stay on the metal and ride into the next tube. The volume is tiny, a fraction of a drop. It is still enough to move a number.
A concrete example. The lavender tube's additive is a potassium salt. Draw the lavender tube before the green one and a trace can carry over, and the potassium reported from that green tube comes back higher than the patient's actual potassium. If nobody catches it, the response is treatment for a dangerous potassium level in someone whose potassium was fine. Redrawing costs one stick. Acting on the wrong number costs more.
The sequence is arranged so that every additive that would ruin a later test is drawn after the tests it would ruin. That is the whole idea. There is nothing clever about it, which is exactly why it works, and why doing it out of order fails quietly rather than loudly.
The sequence follows the widely used convention set out in the CLSI GP41 venipuncture standard. That standard is a paid, copyrighted document, so nothing here is reproduced from it. The sequence itself is a fact, and it was checked against these public sources, retrieved 2026-08-14:
Order of Blood Draw · Cool Toolbox · made by chuck design · chuckdesign.com
The order applies to butterflies and syringes too. A winged set holds air in its tubing that can leave the first tube short, so many labs draw a small discard tube first when a light blue tube leads, and with a syringe draw the order is simply the order you fill the tubes afterward.
Hemolysis is the other way a good stick produces a bad result. Red cells that rupture during collection spill their contents into the sample, which falsely raises potassium, LDH and AST, and usually gets the specimen rejected. The usual causes are a needle that is too narrow, too much vacuum pull on a small vein, and shaking a tube instead of inverting it gently.
Fill and mix still matter after the order is right. Additive tubes are calibrated to a full tube of blood, and the additive only works once it is mixed through, which is what the gentle inversions are for.
The sequence on this page was checked on 2026-08-14 against the four public references listed above: CLSI's own summary of the draw order, the Center for Phlebotomy Education, the StatPearls chapter on laboratory tube collection, and the WHO phlebotomy best practice guidance. Tube colors and additives are industry facts published by every tube manufacturer and lab.
The CLSI GP41 standard itself is a paid document under copyright. Its text is not reproduced or paraphrased here. Everything above is written from the publicly documented convention in our own words. If your lab has a copy of the standard, it is the more precise reference, and your lab's own chart is the one that governs your practice.