Which tube must be filled to at least 90% for accurate PTT testing?

The blue-stopper tube is specifically designed for the collection of blood samples for coagulation testing, including Prothrombin Time (PT) and Partial Thromboplastin Time (PTT) tests. It contains sodium citrate as an anticoagulant, which helps prevent the blood from clotting during the testing process.

For accurate results in PTT testing, it is crucial that the tube is filled to at least 90% of its total volume. This is because the sodium citrate needs to maintain a consistent ratio with the blood sample to ensure the proper anticoagulation effect. An insufficient sample can lead to a higher ratio of anticoagulant to blood, potentially skewing the results and making them unreliable.

In contrast, the other tubes mentioned have different purposes and anticoagulant characteristics that do not apply to PTT testing. The red-stopper tube typically lacks any anticoagulant, making it unsuitable for coagulation studies. The green-stopper tube usually contains heparin, which is also not appropriate for PTT because it significantly interferes with the testing. The gray-stopper tube often contains oxalate or fluoride, which is used for glucose testing and is not involved in coagulation studies. Thus, the blue-stopper