What does the serum separator tube (SST) contain?

The serum separator tube (SST) is specifically designed to facilitate the separation of serum from blood after centrifugation. The critical feature of the SST is the gel additive it contains, which forms a barrier between the serum and the cellular components of the blood once the tube is spun in a centrifuge. This gel allows for easy collection of the serum for various laboratory analyses while preventing contamination from cellular elements. The utilization of the SST is common in clinical settings where serum samples are required for testing, making its role essential in phlebotomy.

Other options refer to components that serve different purposes. Clotting factors are present in blood but are not unique to SSTs; hematocrit relates to the measurement of the proportion of blood volume that is occupied by red blood cells and does not pertain to the tube's function; sodium citrate is an anticoagulant commonly used in other types of blood tubes, such as those for coagulation studies, rather than for serum separation. This distinction highlights the specific function and purpose of the serum separator tube.