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SAMPLE BOTTLES.
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.
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.
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)
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.
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.
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
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.
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.
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
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.
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.
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
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
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
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.
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.
COMMON TESTS:
glucose - this can be fasting or non-fasting, or part of a glucose tolerance test (GTT)
lactate
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.
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.
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
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.
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.
COMMON TESTS:
ammonia insulin renin and aldosterone
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.
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.
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.
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.
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
