Which color tube needs to be filled completely?

The blue tube is designed for coagulation studies, primarily tests such as PT (prothrombin time) and aPTT (activated partial thromboplastin time). It contains sodium citrate as an anticoagulant. One of the essential requirements for accurate test results with the blue tube is that it must be filled to the proper volume to maintain the correct blood-to-anticoagulant ratio.

If the tube is not filled completely, it can lead to an insufficient volume of anticoagulant in comparison to the blood, which can result in inaccurate coagulation test results. The blue tube is specifically calibrated to ensure the reliable performance of these tests; hence, adhering to the fill requirement is critical to obtaining valid and reproducible results. This is not a requirement for all types of collection tubes, which makes the blue tube unique in this respect.