Final answer:
For a PT/PTT test, a phlebotomist should select a tube containing sodium citrate anticoagulant. This is because sodium citrate prevents clotting by binding calcium, which is necessary for the coagulation process, ensuring accurate test results for evaluating clotting tendency.
Step-by-step explanation:
A phlebotomist should select a tube containing sodium citrate as the anticoagulant to collect a sample for a PT (Prothrombin Time) or PTT (Partial Thromboplastin Time) test. These tests are used to evaluate the clotting tendency of blood in the pathway of coagulation. The sodium citrate works by binding calcium in the blood, which is necessary for blood clotting, thus preventing the blood from clotting in the tube. It is essential to use the correct anticoagulant to ensure accurate test results because different anticoagulants affect different parts of the coagulation pathways.
Blood collected into tubes containing other anticoagulants like EDTA or lithium heparin, which are used for different types of analyses, would not be suitable for PT/PTT testing. EDTA binds calcium and is typically used for complete blood count (CBC) tests, while lithium heparin works by activating antithrombins, thereby inhibiting thrombin and other clotting factors, which is useful for obtaining plasma without clotting for various chemistry tests.