What Laboratory test requires blood collection in a citrate tube?

• A. Thrombin Time
• B. Prothrombin Time
• C. Fibrogen
• D. Fibrin Degradation Products

Answer: (B)

Blood collection in a citrate tube is used to obtain plasma by preventing clotting until analysis. Citrate binds calcium, keeping coagulation factors from triggering clots inside the tube. Prothrombin Time is the test that uses this citrated plasma to assess the extrinsic/common coagulation pathway. In the assay, tissue factor and calcium are added to the citrated plasma to start clotting, and the time to clot formation is measured. The citrate tube is essential because it preserves the plasma and its clotting factors long enough for an accurate measurement. While other coagulation tests can also use citrated plasma, this test is specifically designed to be performed on plasma from a citrate-anticoagulated tube, making it the best fit for the requirement.