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Choosing The Right Blood Collection Tubes

So you’re designing a project using human blood samples. Maybe you’re studying blood cells using hematology microscopy, maybe you’re after genetic material or circulating biomarkers. For many basic scientists, the process of getting that blood out of a person and into your project can be intimidating.

Where Do You Start?

Whether you’re collecting your samples in-house or through a clinic, hospital or pathology center, you’ll need to have a good idea of what kind of blood collection tubes suit your purposes. The first thing to check is your protocol – for example, some ELISAs will specify the types of samples you can and can’t use.

But what if your protocol doesn’t specify, or you’re adapting a method from another system, or you just want to make sure you’re storing the best type of sample for future not-yet-defined analyses? Hopefully, I can help you start to find your way around all those differently-colored tubes.

(A quick note about those cap colors before we begin: I’ve listed them below, and the color-coding system is generally pretty consistent, but I can’t promise the colors are the same in every company producing blood collection tubes.)

Serum Tubes

Probably the first thing to figure out is whether you are after serum, or whether you’ll need to stop the blood from clotting. Don’t get serum confused with plasma – while they’re both the liquid, cell-free part of the blood which can be obtained by centrifugation, the key difference is that serum is the product of blood which has been allowed to clot, while in a plasma sample, the dense cells are simply spun to the bottom.

So serum is, in simple terms, what remains in the blood after it clots: a cell-free liquid that is also depleted of coagulation factors. It can be a good, stable way of measuring the blood’s proteins, lipids, hormones, electrolytes and so on. Many of these markers can be stored for days in the fridge, or frozen down and measured in batches later.

  • Serum (clot activator) tubes (color dependent on brand; BD is commonly gold but also red, Greiner is red). These tubes have silica particles, which activate clotting. Some also have a gel to separate the serum. Those without the separating gel are potentially more useful in sensitive diagnostic testing. If you’re looking for a protein that isn’t involved in coagulation, this is a good place to start.
  • Thrombin-based clot activator tubes (orange). Although the silica-coated tubes clot within about 30 minutes, the orange tubes clot within 5. They’re mainly used clinically for tests that are needed especially quickly. However, some of the serum components are a little less stable in these tubes.

Anticoagulant Tubes

This is the category to consider if you need cells or plasma (a cell-free liquid which still contains coagulation factors).

EDTA (Purple)

EDTA prevents clotting by chelating calcium, an essential component of coagulation. This is your basic hematology tube (by which I mean identifying and counting blood cells, blood typing etc). Plasma stored from EDTA blood can also be used to measure most proteins, and genetic material can easily be stored from EDTA buffy coats (the interface between the red cells and the plasma after centrifugation, containing white cells and platelets). Note: these tubes contain either K2EDTA or K3EDTA.

Sodium Citrate (Light Blue)

For coagulation and platelet function tests. Like EDTA, citrate acts by removing calcium from the blood. Unlike EDTA, it’s reversible – so calcium can be added back to study coagulation under controlled conditions. Citrated plasma is also used to measure coagulation-relevant factors. It’s worth noting that a citrate tube should not be the first type of tube filled after venepuncture – the first few mL of blood drawn will be a bit activated. If you only need citrate for your project, then you should collect a discard tube first. Also, note that different concentrations of citrate are available from different companies.

CTAD (Also Light Blue)

CTAD stands for citrate, theophylline, adenosine and dipyridamole. These aren’t very commonly used, but are worth knowing about – they prevent ex vivo activation of your platelets, making them useful for some more sensitive platelet function and coagulation studies. Note that CTAD is light-sensitive, so keep these guys in the dark.

Lithium/Sodium Heparin (Green)

Similar in use to serum clot activator tubes, but suitable for tests in plasma rather than serum. Like the serum tubes, heparin tubes can also come with a separating gel. Heparin acts by inhibiting thrombin formation. Note: if your endgame is PCR, you should know that heparin is particularly known to interfere with PCR reactions. However, whichever anticoagulant you choose, you may need to allow for it in your reaction mix.

Sodium Fluoride (Color Dependent on Brand; BD is Grey, Greiner is Black)

Sodium fluoride is an antiglycolytic agent, so these tubes are used for glucose and lactate testing. They also contain an anticoagulant (there are different types available).

Acid Citrate Dextrose – ACD (Yellow)

These ones are not common, but they are used for blood and tissue typing and DNA analysis.

Sodium Polyanethol Sulfonate -SPS (Also Yellow)

SPS stabilizes bacterial growth. Useful for microbiology.

For specific purposes, there are more blood collection tubes out there, but hopefully, this has given you a handle on where to start. Good luck, and welcome to the world of – let’s be honest – feeling just a little bit like a vampire.

Image Credit: Caroline Reddel


  1. Winston Crawford on May 10, 2019 at 5:45 pm

    I need to order a small qantity, less than 100, of K2EDTA tubes. Can take larger number if minimum order is required. Any ideas?

  2. Mo Talebi on November 29, 2018 at 2:37 am

    Thanks for the useful summary. Just a quick question. I have blood samples collected in BD vacutainer lavender cap tubes (K2-EDTA) for testing against chemical contaminants. Tubes kept in the fridge for a while and now aimed for analysis. However, the blood inside now look separated in two phases, half dark red liquid, half dark red solid (clotted?). Does this mean blood has been clotted in the tubes or the solid matter is just red cells, etc? more importantly, can I assume that the top liquid part is plasma? Thanks!

  3. Adam Jones on April 2, 2018 at 2:12 pm

    There is a great resource on the order of draw and the phlebotomy career at http://www.ephlebotomytraining.com. I have been a phlebotomist for about 5 years and knowing the correct tubes and colors is an important part of drawing blood.

  4. shilpa subash on March 1, 2018 at 1:39 pm

    Can I separate serum if I collected blood from slaughter house ? Is sterile equipments necessary?

    • Josh on March 21, 2018 at 11:26 pm

      Depends on how you are collecting the blood. If it is not directly from the source (animal), you are likely to have some issues with the purity and testability of the samples. From a scientific standpoint, it makes more sense to collect an IV sample than to collect the sample from say the ground. Assuming that you are collecting an IV sample, you need to use an SST, red top tube, or a non-additive tube that does not inhibit clotting. From those tubes, you can separate the serum once the sample has been centrifuged.

      If you are collecting the sample from an animal that is about to be slaughtered, it is not necessary to prep a sample site through sanitization unless your focus is on microbiology. When a human sample is collected, the prep of the site with alcohol is to reduce the chance of infection or in a more rare case, phlebitis. When a blood culture is being collected, a more aggressive approach is used to decrease the microbial population of the skin with things like chlorhexidine gluconate.

  5. Aaron Bridge on February 9, 2018 at 1:08 am

    What colour tubes would I use to analyze amino acids (mainly EAA and BCAA) in the blood.

  6. Christian on September 6, 2017 at 2:07 pm

    Thanks for that very nice intro, but how does one choose between lithium and sodium heparin? And between sodium, K2, and K3 EDTA? Are there any general advice on this for measuring cytokines, antibodies, etc.?

    I have asked many but nobody seems to know, and I have yet to see e.g. ELISA kits specifying this although there must be a reason for the vendors to bother making all these different formulations. Maybe the differences are only relevant in very special cases/tests?

  7. AMG on August 16, 2017 at 11:57 pm

    What about red top?

    • Siva on August 24, 2017 at 7:40 am

      RED one is Serum tubes….That is detailed in above

  8. Heather on July 31, 2017 at 5:14 pm

    Thanks for the explanation…. But I must know, where did you find that mug?!!

    • Caroline Reddel on November 29, 2017 at 4:37 am

      Isn’t it great? It was made for me by some students.

  9. Rehab on July 26, 2017 at 6:24 pm

    thnx yes it was useful for the vampire world 🙂

  10. Dharmendra kumar on May 23, 2017 at 9:32 am

    Good acknowledge

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