What is critical for the fill ratio in a blue stoppered tube?

The blue stoppered tube is typically used for coagulation studies, particularly for testing prothrombin time (PT) and activated partial thromboplastin time (aPTT). The correct fill ratio for these tubes is essential because an improper fill can lead to erroneous test results. Specifically, the optimal fill ratio of 1:5 is critical because it ensures that the ratio of blood to anticoagulant (sodium citrate in this case) is appropriate for accurate laboratory results.

When blood is drawn into the tube, the anticoagulant must be in sufficient quantity to effectively bind calcium ions and prevent clotting. A ratio of 1:5 indicates that for every 1 part of sodium citrate, there should be 5 parts of blood. This precise ratio helps maintain the necessary ionic concentration to preserve the function of the blood components during testing.

Understanding the importance of this fill ratio reinforces the need for proper collection techniques to ensure valid results in coagulation tests, which can influence patient management and treatment decisions.