A light-blue top tube (a blood collection tube containing 3.2% sodium citrate) that will be used for coagulation testing must be filled to completion. Under-filling the tube changes the ratio of blood to anticoagulant. This can affect the accuracy of coagulation tests that are performed using this specimen.
If a winged blood collection device (butterfly) is used to collect a light-blue top tube for coagulation studies, a waste tube should be drawn first. The waste tube must also be a light-blue top tube or a tube that contains no additives. This waste tube is drawn first to remove the air in the tubing of the winged collection device. Once blood flows through the tubing, the waste tube can be removed and discarded. The waste tube does not need to be completely filled. If the air is not displaced from the tubing into a waste tube, it will be drawn into the tube used for testing and cause a short-fill of the tube. Less volume of blood in the tube alters the required blood to anticoagulant ratio needed for coagulation studies.