What is the purpose of the thixotropic gel?

• A. Inhibits coagulation
• B. Additive used to separate cells from plasma during centrifugation
• C. Preserves glucose
• D. Lyses red blood cells

Answer: (B)

Thixotropic gel is designed to create a physical barrier between the cellular portion and the plasma or serum after centrifugation. Its density is chosen so that, when spun, it moves to sit between the separated cells and the liquid, preventing them from mixing and protecting the analytes from cellular metabolism or contamination. Because the gel is inert, it does not inhibit coagulation—that function comes from anticoagulants—nor does it preserve glucose or lyse red blood cells; those roles are handled by other additives. Therefore, its purpose is to separate cells from plasma during centrifugation by forming a stable barrier.