NHCO Order of Draw Practice Test

SST tubes rely on a clot activator to speed up serum production and then a gel barrier to keep the serum separate from the clot. The additive here is silica with Celite, which provides surfaces that rapidly activate coagulation. When blood clots quickly, the gel separator that sits in the tube during centrifugation moves between the serum and the clot, giving a clean, isolated serum sample for testing. The other substances listed aren’t used for this purpose in SST tubes: sodium fluoride is for glycolysis inhibition in fluoride tubes, ethylene glycol isn’t a standard phlebotomy additive, and potassium oxalate is an anticoagulant used in other tube types, not SST.