What is the purpose of the serum separator in a serum separator tube (SST) used for routine chemistry?

• A. To speed up clotting
• B. To clot the blood faster
• C. To separate serum from cells after clotting
• D. To anticoagulate the blood

Answer: (C)

The key idea is how the gel in a serum separator tube creates a physical barrier between serum and blood cells after centrifugation. Once the blood clots, centrifugation drives the gel to position itself between the liquid serum and the cellular portion. That barrier keeps serum relatively free from cellular components and metabolic byproducts, which helps preserve the serum’s composition for accurate routine chemistry tests. The gel’s role is not to speed clotting or to anticoagulate; clotting is aided by the tube’s clot activator, and the separator’s job is the separation after clot formation. This separation also improves sample stability during handling and transport.