What is the purpose of the serum separator gel in SST tubes?

• A. To separate serum from cells after centrifugation for cleaner serum
• B. To prevent clotting
• C. To preserve glucose
• D. To inhibit bacteria

Answer: (A)

Serum separator gel’s job is to form a physical barrier between the serum and the clot’s cellular components after centrifugation, giving you cleaner, more stable serum. The gel, which is thixotropic, moves into position during spinning to sit between the liquid serum and the coagulated material, so the serum can be drawn off without carrying red cells, white cells, or clot remnants. This separation helps prevent cellular metabolism from altering serum constituents and makes aliquoting and transport easier and safer.

It doesn’t prevent clotting—that’s handled by the clot activator in the tube. It also doesn’t preserve glucose (that requires glycolysis inhibitors in other tube types), and it isn’t designed to inhibit bacteria.