Final answer:
An SST tube should be inverted 5 times to mix the blood with the gel and separate the serum.
Step-by-step explanation:
In the field of biology, the abbreviation 'SST' typically refers to a Serum Separator Tube. Inverting the tube helps to mix the blood with the gel in the tube, which separates the serum from other components. The recommended number of inversions for an SST tube is 5 times to ensure adequate mixing of the blood and gel.