Final answer:
For PT or PTT, use a tube with sodium citrate, invert it gently multiple times, centrifuge as per guidelines, and ensure correct blood-to-anticoagulant ratio for accurate results.
Step-by-step explanation:
When drawing blood for Prothrombin Time (PT) or Partial Thromboplastin Time (PTT) tests according to the Clinical and Laboratory Standards Institute (CLSI)/National Committee for Clinical Laboratory Standards (NCCLS), it's crucial to use the correct type of blood collection tube. For these coagulation tests, blood should be collected into a tube containing sodium citrate, not tubes with EDTA, heparin, or other anticoagulants which are not appropriate for coagulation studies.
Once collected, the tube should be gently inverted several times to mix the anticoagulant with the blood properly. After that, the blood sample should be centrifuged at the specified speed and duration to obtain good quality plasma typically free of cells. This plasma is used for the PT and PTT tests.
It is also essential to fill the tube to the proper volume, as the ratio of blood to sodium citrate is critical for accurate test results. Underfilled or overfilled tubes can lead to incorrect results. As per CLSI guidelines, the ratio of anticoagulant to blood should be 1:9.