Color Coded Test Tubes

Have you ever wondered about the rainbow assortment of test tubes that the lab uses for blood draws?  I remember the time my rheumatologist marked twenty-five different boxes on the lab order slip, and the vampire phlebotomist took forever counting out specific numbers of different colored tubes.  That was when I realized that color matters.  Every color stands for a specific additive, so it’s important to get the right one.

Test tubes usually have additives to make blood behave in specific ways until it can be tested.  Some additives cause blood to clot, others prevent it from clotting.  Different chemicals are used for different lab tests.

Tests requiring serum are drawn into a test tube containing a clot activator.  The tube will then be centrifuged, and the clot activator ensures that it’s serum (instead of plasma) at the top of the tube.  Depending on the lab, these are generally gold-topped (or plastic red-topped) test tubes (although one lab tech claims that green can sometimes be used, depending on the specific test ordered). Part of the difference is the lab’s machinery and preferences.

Notice that the first thing the phlebotomist does after a draw is to invert the test tube.  This is to make sure that all the chemical on the tube’s stopper is mixed into the blood.

Other colors of tubes contain an anticoagulant to stabilize different blood components so that tests can be run later.  Since those different colors indicate different additives for different tests, and since it’s possible for small amounts of additive from one tube to carry over to the next when tubes are switched, the order in which tubes are drawn is important.  Otherwise, the blood sample could be contaminated and the test results wouldn’t be valid.

Before labs were computerized, the person doing the blood draw had a book to reference so she’d know which color of tube to use.  Now many labs have computers which will print labels stating the patient’s name and date of birth; those labels can also indicate which type of tube should be used to obtain the sample.

According to the Clinical and Laboratory Standards Institute, order of draw is:

  • Sterile Blood Cultures are drawn first
  • Light Blue – for coagulation tests (ie when a person is taking blood thinners)
  • Gold (or Red plastic tubes*)  for tests needing serum instead of whole blood or plasma**
  • Green – for some of the chemistry tests
  • Purple/Violet– hematology tests (CBC, ESR…)
  • Grey– for blood sugar tests

Some labs vary the sequence slightly (ie gold/red before blue), but this is CLSI’s order of draw.  Some people, unfortunately, pay no attention to the importance of order, and bounce back and forth between different colors of tubes.  When that happens, it might be worth taking the time to ask some questions or find a different lab.

My rheumatologist usually orders tests for gold, green, and purple test tubes.  Have you noticed what yours orders?

*Red-topped glass test tubes don’t have any additives and are used for different tests (ie antibody or drug tests) and are a different place in the draw sequence

**Some labs use red/black tiger-striped tops for serum collection.  STAT serum collection can be drawn into tubes with orange or yellow/grey tiger-striped tops.  The tubes that a lab has on-hand will depend on the types of tests that they normally run.


11 thoughts on “Color Coded Test Tubes

  1. I am really finding all of this interesting. I had no idea what they meant but knew they were different. I had no idea about the order being important, but it makes sense now that you explained it.

  2. I knew that the different colors meant different sorts of tests/purposes, but admit that I wasn’t terribly curious about them. I love how you always come up with the most interesting and informative posts, Socks! Once again, you’ve taught me something I’m glad to know about. Thanks. 😉

    That said, how are you? How’s your daughter? You’ve been on my mind.

  3. Went for my quarterly blood tests today and now I know what the vials are for. She also used a vial with a red and black swirled top. Hmmm what was that for?

    • That tube is called a “tiger top”. It is also known as an SST tube. This tube has an additive to clot the blood and allow for only serum to remain at the top of the tube, for testing purposes, once it is centrifuged.

  4. Listen carefully, when you collect a Blue Top tube during a multiple collection before a Red, Yellow or Tiger top tube, the Sodium Citrate (additive inside the blue top tube ) an anti coagulate will saturate the back of a vacutainer needle (the part covered by a sheath) will cross contaminate tubes that has no additive inside (red top) or tubes that has an additive TO CLOT whole blood (that is yellow top, tiger top an etc.). I do not recommend a Blue top tube placed at the top of an order of draw.

    • As stated in the post, the order listed was published by Clinical and Laboratory Standards Institute. I would hope that people doing blood draws follow their labs’ protocols (which I hope would be based on authoritative data). How scary to think that a health professional would consider arbitrarily constructing a draw order off random blogs. …and I suspect that you meant “cross-contact” not “cross contaminate” since there shouldn’t be any bacteria in the tubes.

  5. me and my friend are both curious about the color coding of the test tube but when we read you page it made us realize that it is very important to know its purposes so that if we can be able to encounter these stuff again and again we are no longer ignorant about it. thank you!

    from: alodia and lyn

  6. I need bloods done for a possible ovarian cyst. My hours mean i have to have my bloods taken in work (a nursing home) but as they deal with OAPs they don’t know which colour coded tubes to use. Anyone know???

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