The inert gel of serum separator tubes and plasma separator tubes is designed to provide an intact barrier between the blood cells and the harvested serum or plasma. Those responsible for centrifuging gel-containing tubes should inspect tubes following centrifugation to ensure that the gel barrier is intact and forms a complete barrier between cells and the serum or plasma. Any evidence of contact between blood layers or evidence of "bleeding" from the cell layer through the gel requires attention and corrective actions. Such actions may include checking centrifugation type, speed and timing, monitoring blood volume prior to centrifugation, and assessing samples for adequate clotting (if serum) prior to centrifugation.
