2. INTRODUCTION.
The colours of the Vacutainer bottles are standardized, but
depending which hospital you end up working in there
may be some variation in preferences between individual
laboratories, especially when it comes to tests which are
performed less commonly. I have used as many sources as
possible to compile the information below, so hopefully it
is as accurate as possible, but obviously I cannot
guarantee it will be applicable to all hospitals. Always
check local guidelines if you’re not sure.
3. PURPLE
These bottles are generally used for haematology
tests where whole blood is required for analysis.
ADDITIVE: contains EDTA (ethylenediaminetetraacetic
acid), which acts as a potent anticoagulant by binding to
calcium in the blood. EDTA also binds metal ions in the
blood and is used in chelation therapy to treat iron, lead or
mercury poisoning. Its blood-binding capacity also means it
can be labelled with radioisotopes and used as an EDTA
scan to test renal glomerular filtration rate.
4. COMMON TESTS:
full blood count (FBC)
erythrocyte sedimentation rate (ESR)
blood film for abnormal cells or malaria parasites
reticulocytes
red cell folate
Monospot test for EBV
HbA1C for diabetic control
parathyroid hormone (PTH)
5. TIPS FOR USE:
the purple tube needs inverting about 8 times to
mix the sample with the EDTA. About 1ml of
blood is sufficient to do a full blood count, but to
get an ESR you need a full purple bottle.
6. PINK
The pink bottles work in the same way as the
purple ones, but are specifically used only for
whole blood samples being sent to the
transfusion lab.
ADDITIVE: this tube also contains the
anticoagulant EDTA.
7. COMMON TESTS:
group and save (G&S) - this simply means the patient’s blood is typed and
tested for antibodies, then saved in the lab in case it is required; it DOES
NOT get you blood products for transfusion. If you need blood products
you have to request a crossmatch.
crossmatch (XM) – this means that the patient’s blood is typed and tested
as above, then matched to specific units of blood, platelets or other
products for transfusion. You need to specify on the form how many units
you need, why you need them and when they are required. A full
crossmatch takes about 45-60 minutes in the lab – if you have an unstable
bleeding patient and think you’ll need blood products sooner than this, you
still need to send a crossmatch sample, but you can ask the lab for units of
type-specific blood (which take 10-20 minutes), or in a genuine emergency
you can use their stocks of O negative blood from the fridge.
direct Coomb’s test (aka direct antiglobulin test) for autoimmune
haemolytic anaemia
8. TIPS FOR USE
the pink tube needs inverting about 8 times to mix
the sample with the EDTA. It should contain at least
1ml of blood, but more is preferred by the labs if at
all possible. It has a special label which needs to be
carefully filled in by hand at the bedside to ensure
the correct patient details are used and prevent
potentially catastrophic mismatched blood
transfusions. If you need blood for a patient
urgently, or have any unusual or complicated
requests, you must ring the transfusion lab and let
them know, or you risk invoking their terrifying
wrath.
9. BLUE
The blue bottle is used for haematology tests
involving the clotting system, which require
inactivated whole blood for analysis.
ADDITIVE: contains buffered sodium citrate, which
acts as a reversible anticoagulant by binding to
calcium ions in the blood and subsequently disrupting
the clotting cascade. Sodium citrate is also added to
blood products for transfusion, and acts as a
preservative by stopping them from clotting in the bag.
10. COMMON TESTS:
coagulation screen including bleeding time for platelet
function, prothrombin time (PT) for extrinsic pathway, activated
partial thromboplastin time (APTT) for intrinsic pathway,
and thrombin time (TT) or fibrinogen assay for the final common
pathway
D-dimer for thrombosis e.g. due to DVT or PE
INR for monitoring patients on warfarin (this is calculated from the
prothrombin time)
activated partial thromboplastin ratio (APTR) for monitoring
patients on IV heparin infusions (this is calculated from the APTT)
anti-Xa assay for monitoring patients on high-dose low molecular
weight heparins like tinzaparin
11. TIPS FOR USE:
the blue bottle needs to be inverted 3-4 times to mix the
sample with the anticoagulant. The sodium citrate liquid
in the bottle dilutes the blood sample, and the machines in
the lab are specifically calibrated to interpret results based
on a set ratio of blood to anticoagulant. It is therefore
essential that the bottle is filled to the line marked around
its edge to ensure the tests are interpreted accurately –
otherwise the samples may be over-anticoagulated. Some
clotting tests need to be taken at specific times; INRs
should ideally be done in the morning, and anti-Xa assays
must be taken 3-4 hours after tinzaparin is given. APTR
timings are often indicated on the prescription algorithm.
12. YELLOW
These bottles are used for a huge variety of tests requiring
separated serum for analysis, including biochemistry,
endocrinology, oncology, toxicology, microbiology and
immunology.
ADDITIVE: this tube is known in the lab as the SST (serum
separating tube). It contains two agents; silica particles and a
serum separating gel. The silica particles work to activate clotting
and cause the blood cells to clump together. The serum separator
consists of an inert polymer gel which floats as a layer between
the blood cells and plasma to form a physical barrier between
them. This means that the sample can be centrifuged (spun) in the
lab and the separated serum easily removed.
13. COMMON TESTS:
biochemistry tests are the ones you will encounter most commonly:
urea and electrolytes (U+E) – this includes urea, creatinine, sodium and
potassium
C-reactive protein (CRP)
liver function tests (LFTs) – this includes bilirubin, ALP, AST/ALT, GGT,
total protein and albumin
amylase assay
bone profile - this includes calcium, phosphate, ALP and albumin
magnesium assay
iron studies - this includes serum iron, ferritin, transferrin saturation and
total iron binding capacity
lipid profile – this includes cholesterol, LDL, HDL and triglycerides
thyroid function tests (TFTs) – this includes TSH, free T4 +/- free T3
14. COMMON TESTS:
vitamins e.g. vitamin B12
troponins – this requires 2 samples to be taken at different times to assess
the acute trend
creatine kinase (CK)
urate
serum osmolality – this requires a urine sample to be taken at the same
time
endocrinology: beta-hCG, calcitonin*, cortisol, EPO, sex hormones,
growth hormone, IGF-1
tumour markers: PSA, CEA, CA-125, CA19-9, AFP, lactate dehydrogenase
(LDH)
toxicology: ethanol, cannabis, opiates, benzodiazepines, other drugs e.g.
cocaine, amphetamines
15. COMMON TESTS:
drug levels: paracetamol, salicylates (aspirin),
digoxin, lithium, gentamicin, carbamazepine
microbiology/virology: serology for a wide
variety of bacterial, viral, fungal and parasitic
infections including HIV and viral hepatitis
immunology: immunoglobulins, complement,
autoantibody screen, rheumatoid factor, thyroid
antibodies, α1AT, ACE
16. TIPS FOR USE:
the yellow bottle needs to be inverted about 5 times
to mix the sample with the silica and separator.
Don’t panic if the blood starts to clot or separate in
the bottle, it’s supposed to! The amount of blood
required will depend on how many tests you’re
doing, but at least 1ml is ideal. You can usually get
about 12 tests from one full yellow bottle.
Remember that different labs may be located in
different areas and technicians don’t like sharing –
this means you’ll need to put your biochemistry and
microbiology samples in separate yellow bottles to
go to their respective laboratories.
17. GREY
The grey bottle is only used for two tests, so
compared to the yellow one it’s fairly easy to
remember! It is used for biochemistry tests
requiring whole blood for analysis.
ADDITIVE: contains two main agents. Sodium fluoride
acts as an antiglycolytic agent to ensure that no further
glucose breakdown occurs within the sample after it is
taken. Potassium oxalate acts as an anticoagulant. Some
variants of the grey bottle use EDTA as the anticoagulant
instead.
18. COMMON TESTS:
glucose - this can be fasting or non-fasting, or
part of a glucose tolerance test (GTT)
lactate
19. TIPS FOR USE:
the grey bottle needs to be inverted about 8 times to mix
the sample with the fluoride and oxalate. Only a tiny
amount of blood is required for a glucose, but for a lactate
the bottle should ideally contain at least 1ml of blood.
Venous glucose results are generally more accurate than
fingerprick BM tests, especially in hyperglycaemic
patients, but can take a while to come back from the lab.
If you need a blood glucose urgently then ask one of the
nurses to do a BM for you on the ward. Samples for
venous lactate need to be sent to the lab immediately.
Again, the results tend to take a while to come back, so if
you’re desparate for a lactate see if you can get access to
an ABG machine that does arterial lactates – these are
often available in A+E or ITU, and take about 2 minutes
to process.
20. RED
The red bottle is less common – it is used for
biochemistry tests requiring serum which might
be adversely affected by the separator gel used in
the yellow bottle.
ADDITIVE: contains silica particles which act as clot
activators.
21. COMMON TESTS:
the use of this bottle varies greatly – some
hospitals use it for many sensitive tests, including
hormones, toxicology, drug levels, bacterial and
viral serology and antibodies, whereas others
seem to only use it for a few very specific
purposes and use the yellow bottle for most
things.
my hospital definitely uses it for ionised calcium,
but not much else
22. TIPS FOR USE:
the red bottle needs inverting 5 times to mix the
sample with the clot activator. There is also
another version of the red bottle made out of
glass, which contains no additives whatsoever.
23. DARK GREEN
This less commonly used bottle is for
biochemistry tests which require
heparinised plasma or whole blood for
analysis.
ADDITIVE: contains sodium heparin, which acts as
an anticoagulant.
25. TIPS FOR USE:
the green bottle needs to be inverted about 8
times to mix the sample with the heparin. This
bottle cannot be reliably used to assess sodium
levels.
26. LIGHT GREEN
This rare species of bottle is used for biochemistry
tests requiring separated heparinised plasma. I
have never actually used one but have seen them on
the dermatology ward.
ADDITIVE: this bottle is known as the plasma separator
tube (PST). It contains lithium heparin, which acts as an
anticoagulant, and a plasma separator gel similar to that
used in the yellow bottle, which acts to separate out the
plasma layer.
27. COMMON TESTS:
it can be used for routine biochemistry, but most
hospitals seem to use the yellow bottle for this. It
can also be used for blood ethanol provided the
sample is not for legal purposes.
28. TIPS FOR USE:
the light green bottle needs inverting about 8
times to mix the sample with the heparin and
separator. This bottle cannot be reliably used to
assess lithium levels.
29. OTHERS
dark blue – used for toxicology and trace elements such as zinc, selenium
and copper (however, the ever-versatile yellow bottle can also be used for
these)
tan – used to test for lead
orange – contains a thrombin-based clot activator which allows stat serum
testing
light yellow – used for HLA phenotyping, tissue typing, DNA analysis and
paternity testing
white – used for molecular diagnostics such as PCR and DNA amplification
studies
black - for paediatric ESR
clear lid – used as a discard tube, for example when taking bloods from a
central line
