CPT (Certified Phlebotomy Technician) Practice Exam

The blue top tube is primarily used for coagulation tests due to its specific additive, sodium citrate, which plays a crucial role in the coagulation process. Sodium citrate acts as an anticoagulant by binding calcium ions in the blood, which is essential for the blood clotting process. By using this tube, it allows for accurate measurement of coagulation factors without interference from platelets or other components that might be activated in the presence of calcium.

In contrast, the other tubes serve different purposes based on their additives. The green top tube generally contains heparin, which is also an anticoagulant but is typically used for different types of tests, such as chemistry tests, rather than coagulation specifically. The red top tube is used for serum tests since it does not contain any additives that would affect the integrity of serum. The lavender top tube is commonly used for hematology tests, such as complete blood counts, and contains EDTA, which is not suitable for coagulation studies. Therefore, the blue top tube is the standard choice for coagulation tests due to its composition and functionality.