Blood Tube Colours and the Order of Draw, Explained

Which tube each test needs, the order to fill them in, and why the wrong cap colour — an FBC in a citrate tube, say — gives a wrong result rather than no result.

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Also called Blood tube colours, Order of draw, Vacutainer colours, Blood test tube colours

Published: 15 October 2026

The common tubes and what they hold

The cap colour tells you the additive inside, and the additive decides which tests the blood is fit for. Most clinics in Malaysia use tubes coded like the table below.

Common colour code. Inversion counts are BD’s; other makers differ slightly — follow the insert of the tubes you use.
Cap	Additive	Used for	Inversions
Light blue	Sodium citrate 3.2% — 9 parts blood to 1 part citrate	PT/INR, APTT, D-dimer and other clotting tests	3–4
Red	Nothing (glass) or clot activator (plastic)	Serum chemistry and serology	5 for plastic; none for plain glass
Gold or yellow	Clot activator and separator gel	Serum chemistry — liver and renal profiles, lipids, serology	5
Green	Lithium or sodium heparin	Plasma chemistry when a quick result is needed	8–10
Lavender or purple	K2 or K3 EDTA	FBC, blood film, reticulocytes, HbA1c	8–10
Grey	Sodium fluoride with potassium oxalate	Glucose — the fluoride stops cells using it up	8–10
Black	Sodium citrate — 4 parts blood to 1 part citrate	Westergren ESR	As the maker states

The order of draw

When several tubes are filled from one venepuncture, a trace of additive carried on the needle into the next tube can change its results. The CLSI GP41 standard sets the sequence below. With a winged (butterfly) set, draw a discard tube before the citrate tube so the air in the tubing does not leave it under-filled.

Order	Tube	Why it sits here
1	Blood cultures and other sterile samples	Drawn first so nothing can contaminate them
2	Light-blue citrate	Clot activator and EDTA both upset clotting tests, so citrate comes before them
3	Red or gold serum tubes	Clot activator must not be carried into the citrate tube
4	Green heparin	Heparin carried forward would affect serum and clotting results
5	Lavender EDTA	EDTA carried into a serum or heparin tube falsely raises potassium and lowers calcium
6	Grey fluoride	Fluoride and oxalate damage cells and interfere with other tests

Why an FBC in a citrate tube is wrong

The light-blue tube holds liquid citrate, one part to nine parts blood, so the sample is diluted by about 10%. The analyser cannot tell; it prints a confident, wrong number. Analysers are also set up and verified for EDTA blood, not citrate.

What it does to the result

White cells, red cells, haemoglobin, haematocrit and platelets all read about 10% low. A patient on the edge of anaemia, or a dengue patient whose platelets and haematocrit are being tracked, can be misread.

The one planned exception

When EDTA makes a patient’s platelets clump, a laboratory may run a platelet count from a citrate tube on purpose — filled exactly to the line, run promptly and multiplied by 1.1 to correct for the dilution — and say so on the report.

Platelet clumping and the citrate count

If it has already happened

Do not report the result. Recollect into an EDTA tube. Never pour blood from one tube into another: the additive and the blood-to-additive ratio are then both wrong.

Fill, mix and label

Let vacuum tubes fill until they stop on their own; the additive is measured for the stated volume.
Under-filled citrate tubes are rejected for clotting tests, because excess citrate falsely prolongs clotting times.
An under-filled EDTA tube leaves excess EDTA, which shrinks red cells and lowers the haematocrit and MCV.
Invert each tube gently straight after filling, the number of times its maker states. Never shake.
Label every tube beside the patient with two identifiers, before the patient leaves the chair.
Do not top up a short tube from another tube.

Common mix-ups at the clinic

Mix-up	What goes wrong	Fix
FBC drawn into the light-blue citrate tube	Every count about 10% low	Recollect in EDTA
Glucose sent in a plain or gel tube that waits for hours	Glucose falls as cells keep using it	Use a grey fluoride tube, or separate the sample promptly
EDTA drawn before the serum tube	Falsely high potassium and low calcium on chemistry	Follow the order of draw
A new brand of tubes arrives	Cap colours can differ between makers, and some tube ranges use a different code altogether	Read the additive on the label and brief staff whenever the supplier changes
Citrate tube drawn first through a butterfly set	Under-filled tube and falsely prolonged PT and APTT	Draw a discard tube first

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Frequently asked questions

What colour tube is used for an FBC?

A lavender or purple-top tube containing K2 or K3 EDTA. Cap colours can vary between tube makers, so check that the label says EDTA.

Can an FBC be done from a citrate tube?

Not routinely. Citrate dilutes the blood by about 10%, so every count reads low. The exception is a platelet count deliberately taken in citrate when EDTA makes platelets clump, corrected by multiplying by 1.1 and noted on the report.

What is the correct order of draw?

Under CLSI GP41: blood cultures, then light-blue citrate, then serum tubes (red or gold), then green heparin, then lavender EDTA, then grey fluoride.

Which tube is used for blood glucose?

Usually the grey-top tube with sodium fluoride and potassium oxalate, which stops blood cells using up glucose while the sample waits.

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