NHA Phlebotomy Certification Practice Exam

What chemical or additive is needed for performing an activated partial thromboplastin time?

1. EDTA

2. SPS

3. Clot activator

4. Sodium citrate

The correct answer is: Sodium citrate

The activated partial thromboplastin time (aPTT) test is used to evaluate the intrinsic and common pathways of the coagulation cascade. To accurately perform this test, it's crucial to use a specific anticoagulant that prevents the blood from clotting while allowing the process of testing for clotting factors. Sodium citrate is the correct choice because it acts as an anticoagulant by binding calcium ions in the plasma. Calcium ions are essential for the coagulation process, and by removing them, sodium citrate effectively prevents clot formation. This allows clinicians to accurately measure the time it takes for blood to clot in response to the intrinsic pathway stimuli used in the aPTT test. In contrast, other additives, such as EDTA, are used for different types of tests (like complete blood counts) but may interfere with clotting factor evaluations. SPS is a preservative used for blood cultures and does not serve the purpose of anticoagulation for coagulation tests. Clot activators are intended to promote clotting, which would be counterproductive for aPTT analysis. Therefore, sodium citrate is the appropriate additive for obtaining reliable aPTT results.