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Knowing which blood bottles to use for different tests may not be that important for passing your finals, but will be absolutely essential when you start work on the wards afterwards. It is one of those practical things which tends to be poorly taught at medical school, if at all. Instead, you are seemingly expected to just pick it up on your first day as a junior doctor, when taking blood tests correctly will suddenly become a massive cornerstone of your workload. Even though most hospitals now have printable stickers for bottles which tell you which ones to use, it is still vital to have a basic understanding of which bottles are used and why to prevent embarrassing mistakes and/or awkward phone calls from the lab.
The colours of the vacutainer bottles are standardised, 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 blood bottles are generally used for haematology tests where whole blood is required for analysis.
Purple blood bottles contain 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 assess renal glomerular filtration rate.
Commontests performed using the purplebloodbottle include:
Full blood count (FBC)
Erythrocyte sedimentation rate (ESR)
Blood film for abnormal cells or malaria parasites
Red cell folate
Monospot test for EBV
HbA1C for diabetic control
Parathyroid hormone (PTH)*
Less common tests
Less commontests performed using the purplebloodbottle include:
Some viral PCR tests
Fasting gut hormone screen*
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 perform a full blood count, however, to get an ESR you will need a full purple bottle.
Pink blood bottle
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.
Pink blood bottles also contain the anticoagulant EDTA.
Commontests performed using the pinkbloodbottle include:
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 (a.k.a. direct antiglobulin test) for autoimmune haemolytic anaemia.
Less common tests
Less commontests performed using the pinkbloodbottle include:
Testing for specific red cell antibodies (usually 3 bottles are required).
Haematology tests such as FBC (if the ward runs out of purple bottles).
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, preventing 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 wrath.
For more details on performing blood transfusions safely see our OSCE guide.
Blue blood bottle
The blue bottle is used for haematology tests involving the clotting system, which require inactivated whole blood for analysis.
Blue blood bottles contain 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.
Commontests performed using the bluebloodbottle include:
Coagulation screen: including bleeding time for platelet function, prothrombin time (PT) for assessment of the extrinsic pathway, activated partial thromboplastin time (APTT) for assessment of the intrinsic pathway, and a thrombin time (TT) or fibrinogen assay for assessment of the final common pathway.
D-dimer to assist with ruling out thrombosis (e.g. deep vein thrombosis).
INR for monitoring patients on warfarin (this is calculated from the prothrombin time).
Activated partial thromboplastin ratio (APTR) for monitoring patients on intravenous heparin infusions (this is calculated from the APTT).
Anti-Xa assay for monitoring patients on high-dose low molecular weight heparins like tinzaparin.
Less common tests
Less commontests performed using the bluebloodbottle include:
Specific clotting factors (e.g. factor VIII, factor IX, von Willebrand factor)
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.
If your first bottle is light blue and you are using a butterfly needle you will likely need to use two of these blood bottles to obtain a full sample. This is because when you attach the first bottle it will draw in air from the tubing, resulting in a sample that is unable to fill with enough blood to reach the required level. To avoid this, you can initially attach a light blue blood bottle to remove the air (i.e. fill the tubing with blood), then detach this and fill a second blue blood bottle to the required level.
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 blood bottle (a.k.a. gold)
These bottles are used for a huge variety of tests requiring separatedserum for analysis, including biochemistry, endocrinology, oncology, toxicology, microbiology and immunology.
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&Es): 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.
Bone profile: this includes calcium, phosphate, ALP and albumin.
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 and sometimes free T3.
Vitamins: including vitamin B12.
Troponins: this requires 2 samples to be taken at different times to assess the acute trend.
Creatine kinase (CK)
Serum osmolality: this requires a urine sample to be taken at the same time.
Endocrinology tests that can be performed using a yellow blood bottle include:
Tumour marker tests
Tumour marker tests that can be performed using a yellow blood bottle include:
Lactate dehydrogenase (LDH)
Toxicology tests that can be performed using a yellow blood bottle include:
Other drugs (e.g. cocaine, amphetamines)
Drug level tests
Drug level tests that can be performed using a yellow blood bottle include:
The yellow blood bottle can be used to test for a wide variety of bacterial, viral, fungal and parasitic infections including HIV and viral hepatitis.
Immunology tests that can be performed using a yellow blood bottle include:
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 blood bottle
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.
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.
Commontests performed using the greybloodbottle include:
Glucose: this can be fasting or non-fasting, or part of a glucose tolerance test (GTT)
Less common tests
Less commontests performed using the greybloodbottle include:
Blood ethanol (if not for legal purposes)
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 test, but to assess lactate levels the bottle should ideally contain at least 1ml of blood. Venous glucose results are generally more accurate than finger-prick capillary blood glucose tests, especially in hyperglycaemic patients, but can take a while to come back from the lab. If you require a blood glucose test urgently then kindly ask one of the nurses to perform a capillary blood glucose 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 desperate to quickly assess a patient’s lactate level 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 blood bottle
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.
The additive in red blood bottles 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 things.
My hospital definitely uses it for ionised calcium, but not much else.
Less common tests
Less commontests performed using the redbloodbottle include:
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 blood bottle
This less commonly used bottle is for biochemistry tests which require heparinized plasma or whole blood for analysis.
The additive of darkgreenbloodbottles contains sodium heparin, which acts as an anticoagulant.
Commontests performed using the dark greenbloodbottle include:
Renin and aldosterone
Less common tests
Less commontests performed using the dark greenbloodbottle include:
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 blood bottle
This rare species of blood bottle is used for biochemistry tests requiring separated heparinized plasma. I have never actually used one but have seen them on a dermatology ward once.
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.
It can be used for routinebiochemistry, 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.
Other blood bottles
Despite 18 months of adventures on the wards, there are still some blood bottles I have not yet encountered. I can only assume this means they are hardly ever used and therefore not ones you’ll need to know in detail.
These other blood bottle types include:
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 blood from a central line.
Blood culture bottles
Blood culture bottles contain a culture medium to encourage the growth of any bacteria in the blood sample. There are different bottles available with culture media for aerobic (bluelid) and anaerobic (purplelid) organisms, alongside a variety of others, including one with a black lid for mycobacterial cultures. Until recently, many hospitals require both aerobic and anaerobic culture samples from a patient, whilst others were happy with just aerobic samples. However, there is now a move towards using the purple top (a.k.a. “burgundy”) anaerobic bottles as the standard receptacle for all blood cultures, as studies have shown that they are more effective. Check local guidelines if you’re not sure.
Tips for use
Blood cultures must be obtained using an aseptic non-touch technique (ANTT) to prevent contamination of the samples with the patient’s skin flora or any bugs that might be lurking on your hands. They should also be taken before any antibiotics are started. The blood culture bottle should always be the first one you fill, and ideally needs 8-10ml of blood to ensure a good chance of catching any organisms (if using an anaerobic and aerobic bottle, the aerobic bottle should be filled first). In a perfect world, you would also take another culture from a different site to maximise the diagnostic yield. The results take about 5 days to come back, so if your patient is septic you need to ring microbiology and start them on some empirical antibiotic treatment in the meantime.
An ABG is a very useful test when you find yourself confronted with a critically unwell patient, as it tells you about their oxygenation, their acid-base balance, and in some cases their potassium and lactate as well, and the results are available within minutes.
Tips for use
ABG syringes contain heparin to prevent the sample from clotting – you need to expel this through the needle before taking your sample. Some fill automatically as the plunger is pushed back by the pressure of the blood coming through the needle, whilst others require you to pull on the plunger yourself to fill the syringe. Try to get the self-filling ones – like those shown above – if you can, as they are infinitely better. Compared to taking venous blood, ABGs are technically more challenging, riskier and much more uncomfortable for the patient. For more details and tips on how to take an ABG, see our guide.
Once you have obtained your sample it needs to be taken straight to the lab, as it will become denatured and useless within 10 minutes. To learn how to interpret an ABG, see our guide.
Tips for easy venepuncture
Invert doesn’t mean shake: be gentle with your samples or they’ll haemolyse.
Tests above with a star (*) next to them need to be sent to the lab immediately on ice – to do this you either need to get a special ice bag directly from the lab or if your ward has an ice freezer you can make one yourself by filling a normal sample bag with crushed ice. If you’re not sure you’re doing it right, ring the lab and check before you take the blood sample.
The bottles can be used for other non-blood fluids too, for example, pleural aspirates, ascitic taps and CSF samples obtained by lumbar puncture. The tests each bottle is used for are the same: the purple one is for cell count, the yellow one is for electrolytes, albumin and LDH, the grey one is for glucose, and blood culture bottles can be used for fluid cultures. Don’t forget to specify on your request form what kind of fluid is in the bottle and which part of the patient you got it from.
If you ever find yourself having to get blood from a child, there are special paediatric blood bottles which are much smaller than the adult ones. The colours can vary compared to adult bottles, so always check with the local lab.
If you are unsure about what you need to do for a particular blood test, ask your friendly local lab technician. They are usually more than happy to give you advice as it means they can prevent you from making mistakes that create lots of hassle and annoying paperwork. It’s also better for you if you check, as it saves you having to do your blood tests all over again if you do it wrong, and saves your patient from the unpleasantness of unnecessary additional stabbings.
Blood bottle summary
We have summarised the different types of blood bottles below organised by the order of draw, including the relevant tests and the number of required inversions.
I hope you found this guide helpful. Good luck!
BD Vacutainer Product FAQs. Available from: [LINK].
BD Vacutainer Venous Blood Collection Tube Guide. Available from [LINK].
UCI Pathology Services Manual. Specimen Tube Containers. Available from: [LINK].