Which tube should be used for drawing a PT and PTT blood test?

The correct choice is the sodium citrate tube for drawing a PT (Prothrombin Time) and PTT (Partial Thromboplastin Time) blood test because it contains an anticoagulant that prevents blood from clotting while still allowing for accurate measurement of coagulation factors. Sodium citrate works by chelating calcium ions, which are essential for the coagulation cascade. This prevents the blood from clotting in the collection tube, ensuring that the plasma can be accurately analyzed for both PT and PTT.

Choosing a tube with the appropriate anticoagulant is critical to ensure that the test results are reflective of the patient's coagulation status. Other tubes, like the EDTA tube, contain anticoagulants that can interfere with the specific tests for PT and PTT. The serum separator tube is used for tests requiring serum, and hence, it can lead to clotting, which is not suitable for coagulation studies. The heparin tube, while also an anticoagulant, is not the preferred choice for PT and PTT tests because heparin affects different pathways of the coagulation cascade and may lead to misleading results for tests measuring prothrombin time.