Final answer:
SST on a collection tube indicates it is a serum separator tube, used for collecting blood for serum-based tests, with a gel inside that separates serum from blood cells after centrifugation.
Step-by-step explanation:
When you encounter SST on a collection tube, it stands for serum separator tube. These tubes are used to collect blood specimens for various blood tests, specifically for serum-based tests. Inside the tube, there is a gel at the bottom that acts as a physical barrier between the blood cells and the serum after centrifugation. When the blood is centrifuged, the gel moves upward to the layer of blood cells, creating serum above it which can be used for tests. SST tubes with the gel separator are particularly useful for clinical chemistry tests, including hormonal assays, drug levels, and various other blood chemistry determinations.