Clot activators in the tube stimulate the clotting process and make the ECP-release less time-dependent. A gel barrier facilitates decanting and eliminates the risk of cells being transferred into the serum. Cells left in serum after centrifugation will leak ECP, resulting in falsely high results. Tube materials (glass, plastic etc.) can influence the clotting speed differently. Tube size / volume will influence ECP levels as the temperature effect is greater on a small volume (37°C down to room temperature).