Blood tube colours and additives
What the common blood tube additives are for, and why the cap colour is only a guide.
Colour is a guide, the additive is the rule
Cap colours indicate the additive inside, but they differ between manufacturers. Go by the additive printed on the tube, and use your receiving laboratory’s handbook to decide which tube each test needs.
Sodium citrate
Used for coagulation tests. The ratio of blood to citrate matters, so the tube must be filled to the line; underfilled citrate tubes are rejected.
Clot activator, with or without gel
Produces serum and is used for many biochemistry and immunology tests. The gel, where present, separates serum from cells after centrifugation.
Lithium heparin
An anticoagulant that produces plasma, used for many biochemistry tests.
EDTA
An anticoagulant that preserves blood cells, used for haematology tests such as a full blood count, and for HbA1c.
Fluoride oxalate
Fluoride stops blood cells using up glucose after collection, so this tube is used for glucose and lactate.
Mixing
Invert each tube gently as the manufacturer instructs. Do not shake.
General information only. Your receiving laboratory's handbook and your employer's procedures take precedence.
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