Choosing the correct blood collection tube is one of the most fundamental steps in accurate blood testing. Use the wrong tube and the sample may be unusable, results unreliable, or the patient may need a repeated venepuncture. For GP practices, pharmacies, hospitals, and other health and wellness clinics providing private blood tests and phlebotomy services, having a clear understanding of the tube colour system and what each additive does is an essential part of day-to-day clinical practice.
The good news is that the colour coding used across most blood collection tubes follows a widely recognised standard. While there are minor differences between manufacturers, the core system is consistent enough to serve as a reliable reference. This guide covers the main tube types, their additives, common uses, and a few practical points around tube selection and order of draw.
How Blood Collection Tubes Work
Most blood collection tubes are vacuum-sealed, which causes blood to draw directly into the tube when a needle is inserted. Each tube is pre-loaded with a specific additive, or in some cases none at all, and the additive determines how the blood behaves after collection and which tests it can be used for.
Some additives prevent the blood from clotting, preserving it as whole blood or allowing plasma to be separated. Others actively encourage clotting, so that serum can be collected once the clot has formed and the sample is centrifuged. The tube cap colour identifies which additive is present, allowing clinical staff to select the right tube quickly without needing to read the label each time.
The table below provides a quick reference for the most common tube colours, their additives, and primary uses. Please note this list is not exhaustive. A more detailed breakdown of each type follows.
Tube Colour | Additive | Primary Use |
Red | Clot Activator | Serum for biochemistry and serology |
Gold | Clot Activator and Gel | Serum separation for routine panels |
Purple | EDTA (K2 or K3) | Haematology, blood counts, HbA1c |
Light Blue | Sodium Citrate | Coagulation studies (PT, APTT, INR) |
Green | Lithium Heparin | Plasma chemistry, urgent biochemistry |
Grey | Sodium Fluoride / Oxalate | Glucose, lactate testing |
Yellow | ACD (Acid Citrate Dextrose) | Blood banking, DNA studies, HLA typing |
White / Clear | None (No Additive) | Discard tube or whole blood samples |
A Closer Look at Tube Types
Red and Gold Tubes (Clot Activator)
Red and gold tubes are used to collect serum, the liquid component of blood that remains after clotting and centrifugation. Red tubes typically contain a clot activator, while gold tubes (often referred to as serum separator tubes, or SST) contain both a clot activator and a gel layer. When centrifuged, the gel forms a physical barrier between the clot and the serum, making the serum easier to pipette and extending its stability for transport and storage.
These tubes are used for a wide range of routine biochemistry, hormone panels, liver and kidney function tests, thyroid function, and serology. The gold serum separator is the more commonly used option in private clinic settings because of the cleaner separation it provides. Both BD Vacutainer Serum CAT tubes and VACUETTE CAT Serum tubes are examples of red serum tubes, along with BD Vacutainer SST II Advance and VACUETTE CAT Serum Separator tubes for gold variants.
Purple Tubes (EDTA)
EDTA (ethylenediaminetetraacetic acid) works by binding calcium ions, which are essential to the clotting process. With calcium removed, the blood is kept in its natural, unclotted state. This makes EDTA tubes the standard choice for haematology, as the blood cells remain intact and can be accurately analysed.
EDTA tubes are used for full blood counts, HbA1c, blood film analysis, and certain infectious disease markers. They come in two forms: K2EDTA, where the additive is in a liquid form, and K3EDTA, where it is a dry spray coating to the inside of the tube. K2EDTA is more commonly used in modern practice as it produces slightly less dilution of the sample. Both forms are widely accepted across laboratories, though it is worth checking with the receiving lab if there is any preference.
VACUETTE K2EDTA Lavender and K3EDTA Lavender tubes are available from Medix Group, alongside BD Vacutainer K2EDTA and K3EDTA tubes in a range of sizes.
Light Blue Tubes (Sodium Citrate)
Sodium citrate binds calcium in a similar way to EDTA but is specifically formulated for coagulation testing. The ratio of blood to citrate is critical: these tubes must be filled to the correct level to ensure an accurate blood-to-additive ratio, so underfilling will produce unreliable coagulation results.
Light blue tubes are used for prothrombin time (PT), activated partial thromboplastin time (APTT), INR, fibrinogen, and D-dimer testing. They are typically the highest-priority tube in the order of draw when coagulation testing is required, collected after any blood culture bottles but before other tube types.
One important practical note: when using a winged blood collection set (butterfly needle) and a citrate tube is the first to be drawn, a discard tube should be collected first. This fills the dead space in the needle tubing and ensures the blood-to-citrate ratio in the citrate tube is not affected. Both BD Vacutainer Sodium Citrate and VACUETTE Sodium Citrate Blue tubes are common examples.
Green Tubes (Heparin)
Heparin acts as an anticoagulant and works by inhibiting thrombin and other clotting factors, keeping the blood in a plasma state. Green tubes are commonly used for urgent biochemistry requests where a quick plasma result is needed, as there is no need to wait for the sample to clot before centrifugation.
Lithium heparin is generally preferred over sodium heparin as the latter can interfere with certain electrolyte tests. Green tubes are suitable for many routine chemistry panels, though they are not appropriate for haematology or coagulation testing.
VACUETTE Lithium Heparin Green tubes are a common example here but confirming the preferred tube and anticoagulant with your laboratory is recommended.
Grey Tubes (Sodium Fluoride)
Grey tubes contain sodium fluoride which inhibits glycolysis, the process by which red blood cells consume glucose after collection. Without this inhibitor, blood glucose levels fall steadily after the sample is taken, which would produce inaccurate results. Grey tubes are therefore the correct choice for fasting glucose, glucose tolerance tests, and lactate testing.
Grey tubes also contain a second additive such as potassium oxalate or K3EDTA acting as a secondary anticoagulant alongside the fluoride. VACUETTE Fluoride/Oxalate Grey tubes and VACUETTE Fluoride/K3EDTA Grey tubes are widely used examples within clinics.
Yellow Tubes (ACD)
Yellow tubes containing ACD (acid citrate dextrose) are used for specialist applications rather than routine blood panels. The combination of citrate, citric acid, and dextrose prevents clotting while also preserving white blood cell viability and DNA integrity, which is why these tubes are used in blood banking, ABO blood grouping and Rh typing, HLA phenotyping, and DNA and paternity testing.
ACD comes in two formulations: Solution A contains a higher concentration of each component than Solution B. The specific solution required will typically be specified by the laboratory or testing protocol.
Both BD Vacutainer ACD-A and VACUETTE ACD-A tubes are examples stocked by Medix Group. These are specialist tubes and less commonly needed in routine private clinic settings, but important for clinics involved in blood banking or genetic testing services.
White Tubes (No Additive)
Tubes with no additive, typically with a white or clear cap, serve a couple of distinct purposes. Where a whole blood sample is required without any anticoagulant influence, such as for certain molecular or immunological tests, a no additive tube provides a clean and sterile collection vessel.
They are also commonly used as discard tubes, often to prime the tubing of a blood collection set containing dead space. An example of this is when a citrate coagulation tube is being drawn first, as described above: drawing a no additive discard tube first ensures the tubing dead space is cleared before the coagulation tube is collected.
Examples of these tubes include VACUETTE No Additive White tubes, as well as BD Vacutainer EST tubes which are smaller in size and intended to be used as discard tubes.
Order of Draw
The order in which tubes are filled during a single venepuncture is an important part of blood collection. Additives from one tube can carry over onto the needle tip and contaminate the next tube if the draw order is not followed, potentially affecting results. The widely used standard order is:
- Discard / no additive tubes (white / clear)
- Coagulation tubes (light blue)
- Serum tubes (red)
- Serum tubes with separating gel (gold)
- Heparin tubes (green)
- EDTA tubes (purple)
- Glycolytic inhibitor tubes (grey)
- Other tubes
This sequence is based on guidance from the Clinical and Laboratory Standards Institute (CLSI) and is widely followed across UK clinical settings. The above list is not exhaustive and placement of tubes not listed should consider the potential of their additive altering results obtained from the next tube.
Some laboratories may have specific requirements or exceptions, so it is always worth checking locally, particularly if samples are sent to a third-party laboratory where their protocol should take precedence.
Brands, Sizes, and Collection Equipment
The same tube types are available from various manufacturers, and in a range of volumes. The right size often depends on the volume required by the laboratory, the analyser being used, or the number of tests being run from a single draw. Smaller tubes are preferable where vein access is limited, such as in paediatric or elderly patients.
Two of the most widely used brands in the UK are BD Vacutainer and VACUETTE. Both are well-established and accepted by the vast majority of UK laboratories. Medix Group stocks tubes from both ranges across the key additive types, as well as PREMIUM variants of VACUETTE tubes which feature a screw cap.
Alongside tubes, the right blood collection equipment is also important for a smooth and safe draw. Compatible blood collection needles are available from both BD Vacutainer and VACUETTE, designed for use with their respective vacuum tube systems. Tube holders are also an essential part of the setup including BD Vacutainer One Use Holders and VACUETTE Standard Holders, as well as VACUETTE QuickShield Holders which incorporate a safety sleeve to help reduce needlestick risk after use. For more on needlestick prevention and post-exposure steps, see our article on preventing needlestick injury.
Blood Collection Tubes Available from Medix Group
Medix Group supplies a wide range of blood collection tubes from both BD Vacutainer and VACUETTE across all the key additive types covered in this guide. Whether you are setting up a new phlebotomy service, running private blood panels from a GP or wellness clinic, or looking to consolidate your supplier for tubes, needles, and holders, get in touch with our team to set up an account.
