Sample bottles

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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 youre not sure.


These bottles are generally used for haematology tests where whole blood is required for analysis.

ADDITIVE:containsEDTA (ethylenediaminetetraacetic acid), which acts as a potentanticoagulant 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 purpletube 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.

PINKThe 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.


group and save (G&S) - this simply means the patients 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 patients 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. Afull crossmatch takes about 45-60 minutes in the lab if you have an unstable bleeding patient and think youll 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 Coombs test (aka direct antiglobulin test) for autoimmune haemolytic anaemia

TIPS FOR USEthe 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 carefullyfilled 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.

BLUEThe blue bottle is used forhaematologytests involving theclottingsystem, which require inactivatedwhole bloodfor analysis.ADDITIVE:contains bufferedsodium citrate, which acts as areversible anticoagulantby 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.


coagulation screenincludingbleeding timefor platelet function,prothrombin time (PT)for extrinsic pathway,activated partial thromboplastin time (APTT)for intrinsic pathway, andthrombin time (TT)orfibrinogenassay for the final common pathwayD-dimerfor thrombosis e.g. due to DVT or PEINRfor 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 assayfor 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 isfilled to the line marked around its edgeto 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.

YELLOWThese bottles are used for a huge variety of tests requiring separatedserum 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.


biochemistry tests are the ones you will encounter most commonly:urea and electrolytes (U+E) this includes urea, creatinine, sodium and potassiumC-reactive protein(CRP)liver function tests (LFTs) this includes bilirubin, ALP, AST/ALT, GGT, total protein and albuminamylase assaybone profile - this includes calcium, phosphate, ALP and albuminmagnesium assayiron studies - this includes serum iron, ferritin, transferrin saturation and total iron binding capacitylipid profile this includes cholesterol, LDL, HDL and triglyceridesthyroid function tests (TFTs) this includes TSH, free T4 +/- free T3

COMMON TESTS:vitamins e.g. vitamin B12troponins this requires 2 samples to be taken at different times to assess the acute trendcreatine kinase (CK)urateserum osmolality this requires a urine sample to be taken at the same timeendocrinology:beta-hCG, calcitonin*, cortisol, EPO, sex hormones, growth hormone, IGF-1tumour 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, carbamazepinemicrobiology/virology:serology for a wide variety of bacterial, viral, fungal and parasitic infections including HIV and viral hepatitisimmunology: immunoglobulins, complement, autoantibody screen, rheumatoid factor, thyroid antibodies, 1AT, ACE

TIPS FOR USE:the yellow bottle needs to be inverted about 5 times to mix the sample with the silica and separator. Dont panic if the blood starts to clot or separate in the bottle, its supposed to! The amount of blood required will depend on how many tests youre 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 dont like sharing this means youll need to put your biochemistry and microbiology samples in separate yellow bottles to go to their respective laboratories.

GREYThe grey bottle is only used for two tests, so compared to the yellow one its 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 agentto 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.


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 youre 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.

REDThe 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.


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 hospital de