ASCP Phlebotomy Technician Certification Practice Exam 2025 - Free Phlebotomy Practice Questions and Study Guide

The specimen collection tube commonly used for hemostasis tests is the one that contains sodium citrate as an additive. Sodium citrate works by binding calcium ions in the blood, which is essential for the coagulation process. By chelating calcium, the tube prevents clotting, allowing for accurate measurement of various hemostatic parameters, such as prothrombin time (PT) and activated partial thromboplastin time (aPTT). This characteristic makes it the preferred choice for tests that evaluate the clotting ability of blood.

In contrast, the other options do not serve the same purpose in hemostasis testing. EDTA is primarily used for hematology tests as it preserves cell morphology, but it does not provide the necessary environment for coagulation testing. Clot activators promote clotting, which is counterproductive for hemostasis evaluations. Heparin, another anticoagulant, is often used for other types of tests, but sodium citrate remains the gold standard for hemostasis tests due to its specific mechanism of action in preserving the sample for accurate analysis.