Interior is spray dried with 1.8mg of anhydrous EDTA per 1mL of blood which acts as a anticoagulant binding the calcium ions and interrupting the clotting cascade Clear as glass with equal or better performance Molded to be virtually unbreakable, providing a better level of safety than glass Tubes should be centrifuged within six hours following blood collection Nonscrew Safety Pull Caps can be removed with a gentle pull