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🧪 Blood bottles
Cap colour, additive, what goes in which — and the order of draw
Check your trust's chart before you trust this one. UK labs use two tube systems, BD Vacutainer and Greiner Vacuette, and although they agree on most caps they do not agree on all of them. What follows is the BD pattern, which is the commoner of the two in England.
The order of draw matters because additive carries over on the needle. Citrate before EDTA, because EDTA carried into a clotting sample raises the APTT and the result gets believed.
Two caps are listed under both names — gold is called yellow and lavender is called purple depending on which health board you trained in. Same tube either way.
The order of draw
| 1 · Blood cultures | Bottles firstBefore any tube, to protect them from additive and from skin flora on the needle. |
|---|---|
| 2 · Light blue | Sodium citratePT, INR, APTT, D-dimer, fibrinogen. MUST be filled to the line — under-filled means a false result, not a rejected one. |
| 3 · Gold / Yellow | Serum + gel (SST)U&E, LFT, bone, lipids, CRP, TFT, troponin, drug levels, PSA. |
| 4 · Green | Lithium heparinAmmonia, cytogenetics, some specialist assays. Not for lithium levels. |
| 5 · Lavender / Purple | EDTAFBC, ESR, HbA1c, reticulocytes, malaria, haematinics by local policy. |
| 6 · Pink | EDTA, crossmatchGroup and save, crossmatch, DAT. Hand-written labelling at the bedside — see the caveat. |
| 7 · Grey | Fluoride oxalateGlucose, lactate, alcohol. Fluoride stops glycolysis, so glucose in any other bottle reads low. |
Things that catch people out
| Separate tube | PTH, ACTH, BNP, troponinSeveral labs want their own EDTA tube for these. Sending one tube for FBC and PTH gets one of them cancelled. |
|---|---|
| Citrate fill line | Non-negotiableThe additive is a fixed volume calibrated to a full tube. Nine-tenths full is a wrong INR. |
| Trace elements | Special tubeZinc, copper, selenium, lead. Ordinary tubes leach metal. Ring the lab. |
| Blood cultures | 8–10 ml per bottleVolume is the single biggest determinant of whether an organism grows. Half-filled bottles miss bacteraemia. |
Crossmatch samples are labelled by hand, at the bedside, from the patient's own identification. Not from a printed sticker, not from the notes, not later at the desk. A pre-printed label on a group and save is how the wrong blood reaches the wrong person, and it is the one bottle on this list that can kill somebody.
If your trust uses Greiner Vacuette the serum and trace element caps differ from those above. Check the chart on the wall.
Source: BD Vacutainer tube guide (CLSI GP41-Ed7 order of draw), NHS trust pathology charts