Order of Draw
Choose the tubes and bottles you are taking and see the order to fill them, with the reason for each place. For nurses, doctors, phlebotomists and students.
1. What are you collecting?
0 chosenType any test to see the sample it needs, then add its tubes to your order.
2. Your order of draw
Your trust’s phlebotomy policy and laboratory handbook come first: they say which tubes your laboratory uses for each test.
3. Why this order?
When several tubes are filled through one needle, the back of the needle pierces each stopper in turn. A trace of blood and additive can ride on the needle, or on the stopper, into the next tube. The order of draw lines the tubes up so that anything carried over does the least harm. It is the same order whether you use a needle and holder, a butterfly, or a syringe with a transfer device.
- Blood cultures: first, so they stay free of contamination.
- Citrate (coagulation, then ESR): before anything with a clot activator or another anticoagulant.
- Serum, with or without gel: before any anticoagulant tube.
- Heparin, with or without gel: before EDTA.
- EDTA: late, because EDTA spoils most other tests.
- Fluoride oxalate (glucose): after EDTA.
- Other tubes (for example ACD, QuantiFERON, PAXgene): after the routine tubes, as the tube or the laboratory says.
What goes wrong when the order is wrong?
| Carried over | Into | What it does |
|---|---|---|
| Skin and stopper organisms | Culture bottles | Contaminated cultures: false positives, antibiotics that are not needed, longer stays. |
| Clot activator (serum tubes) | Citrate | Starts clotting in the tube and shortens the clotting times. |
| Heparin | Citrate, serum | Prolongs the APTT; stops a serum tube clotting fully, leaving fibrin in the serum. |
| EDTA (contains potassium, binds calcium, magnesium, zinc) | Serum, heparin, citrate | Falsely high potassium with falsely low calcium, magnesium and alkaline phosphatase. It can look like a life-threatening result. |
| Citrate | Chemistry tubes | Falsely high sodium and low calcium. |
| Fluoride and oxalate | Other tubes | Raises sodium and potassium, lowers calcium, stops some enzyme tests working and damages blood cells. |
Studies of closed systems used correctly have found carry-over rare, and the commonest cause of EDTA contamination is filling tubes from a syringe or poor technique. The European working group on the preanalytical phase still recommends always following the order.
Spotting EDTA contamination
A very high potassium with a very low calcium (and often a low magnesium and alkaline phosphatase) in a patient who looks well is the classic picture. Many laboratories check for it and ask for a repeat sample. The full blood count is not affected, because EDTA is its own anticoagulant. Never assume a high potassium is contamination: the laboratory and the clinical team decide.
Butterflies, discard tubes and syringes
A butterfly’s tubing is full of air. If a citrate tube is the first tube, that air would take the place of blood, the tube would under-fill and the 9 to 1 ratio of blood to citrate would be wrong. A discard tube (plain, or another citrate tube) is drawn first to fill the tubing; it does not need to be full. No discard tube is needed with a straight needle, or when culture bottles or other tubes come before the citrate tube.
With a butterfly, fill the aerobic culture bottle first, so the tubing’s air goes into it rather than into the anaerobic bottle. With a syringe, the anaerobic bottle is usually filled first.
With a syringe, use a transfer device and fill the tubes in the same order, letting the vacuum draw the blood in. Pushing blood through a needle damages the cells and gives the wrong fill.
Capillary (heel and finger prick) samples
The order is different. Blood from a skin puncture starts to clot as soon as it reaches the air, so a blood gas (if needed) comes first, then EDTA (for an accurate platelet count), then the other anticoagulant tubes, then fluoride, and serum tubes last. There is no needle passing through stoppers, so carry-over is less of a worry than clotting.
Cap colours are not universal
BD Vacutainer and Greiner Vacuette use similar colours (Greiner adds a black ring on standard tubes and a yellow ring on gel tubes). Sarstedt S-Monovette, used by many UK trusts, follows the European colour code: EDTA is red, citrate green, lithium heparin orange, serum white (brown with gel) and fluoride yellow. A red cap means a serum tube in one hospital and an EDTA tube in the next. Go by the additive printed on the label, not the colour, especially when you move between hospitals, use paediatric tubes or a new supplier.
Older books say “coagulation last”
Some older texts put the coagulation tube last, or after a discard tube, because of worries about tissue fluid from the puncture. Current CLSI and European guidance put citrate straight after any blood cultures; a discard tube is needed only when the citrate tube is the first tube through a butterfly (or as a test’s own instructions say).
Good practice that matters as much as the order
- Check the patient’s identity and label each tube at the bedside, straight after filling it. Never pre-label tubes, and follow your transfusion policy for transfusion samples.
- Fill each tube to its line and invert it gently straight away; do not shake it.
- Release the tourniquet as soon as blood flows, and keep it on for no more than about a minute.
- Never take blood from an arm above a running drip.
- Check the expiry date of every tube and bottle.
4. Test yourself
References
- Clinical and Laboratory Standards Institute. PRE02: Collection of Diagnostic Venous Blood Specimens, 8th edition, 2025 (formerly GP41, 7th edition, 2017).
- Joint EFLM-COLABIOCLI Recommendation for venous blood sampling. Clinical Chemistry and Laboratory Medicine 2018; 56(12): 2015–2038.
- Order of blood draw: opinion paper by the EFLM Working Group for the Preanalytical Phase. Clinical Chemistry and Laboratory Medicine 2017; 55(1): 27–31.
- World Health Organization. WHO guidelines on drawing blood: best practices in phlebotomy. Geneva: WHO, 2010.
- UK Health Security Agency. UK Standards for Microbiology Investigations B 37: Investigation of blood cultures (for organisms other than Mycobacterium species).
- Clinical Hematology: Theory and Procedures, 5th edition, chapter 2 (Principles of blood collection), tables 2.1 to 2.4.
- British Society for Haematology. Guidelines for pre-transfusion compatibility procedures in blood transfusion laboratories.
- Makers’ guidance: BD Vacutainer order of draw and tube guide; Greiner Bio-One Vacuette order of draw; Sarstedt S-Monovette instructions for use; QIAGEN QuantiFERON-TB Gold Plus; PreAnalytiX PAXgene Blood RNA tube; Streck Cell-Free DNA BCT. UK NHS trust tube guides for local colours.