Which tube must be completely filled for accurate testing?

The light blue topped tube, which contains sodium citrate as an anticoagulant, must be completely filled for accurate testing, particularly in coagulation tests such as PT (Prothrombin Time) and aPTT (Activated Partial Thromboplastin Time). The reason for this requirement is that the sodium citrate must have a specific ratio to the blood in order to effectively anticoagulate the sample. If the tube is underfilled, the resulting anticoagulant-to-blood ratio will be skewed, potentially leading to inaccurate test results.

On the other hand, other tubes like the red top, tiger top, and mint green top tubes serve different purposes and have different requirements for sample volume. While it is generally good practice to fill them appropriately, they do not necessitate the same strict volume criteria needed for coagulation testing. For instance, red top tubes are used for serum testing and can accommodate a wider range of fill volumes without compromising results. Similarly, tiger top and mint green tubes, which are used for other specific tests, also have their protocols but are not as sensitive to underfilling in the same critical way as the light blue topped tube.