California Phlebotomy Certification Practice Exam

Which of the following tubes is typically used for coagulation studies?

1. Red top tube

2. Green top tube

3. Citrate tube (light blue top)

4. Serum separator tube

The correct answer is: Citrate tube (light blue top)

The citrate tube, often characterized by its light blue top, is specifically designed for coagulation studies because it contains sodium citrate as an anticoagulant. This anticoagulant works by binding to calcium ions in the blood, which is a crucial component for the coagulation process. By preventing blood from clotting, the citrate tube allows for accurate measurement of coagulation factors, providing essential data for diagnostic tests such as prothrombin time (PT) and activated partial thromboplastin time (PTT). Using the light blue top tube ensures that samples remain in a state that reflects the patient’s coagulation status without interference from clot formation, which is crucial for reliable test results. Other types of tubes, such as those with red tops or serum separator tubes, do not contain anticoagulants and are not suitable for this purpose, as they would lead to clotting and yield inaccurate results for coagulation testing. The green top tube, which typically contains heparin, is also used for other types of tests involving plasma but is not standard for coagulation studies.