Ok, this is turning into a pet peeve of mine. Has anyone else noticed that everyone says that the light blue top tubes (for coags) contains heparin? For example, when the lab calls and says the blue tube is clotted, someone immediately says "how can that be with heparin in the tube?" According to the tubes and the website of the company that makes the tubes, the blue tubes contain "buffered sodium citrate," and this citrate prevents clotting. While it is true, they a properly inverted tube should not clot, there is no heparin in the tube (at least until the blood is added ).