Gel and Clot Tubes are used to collect blood for clinical biochemistry and immunology. They can improve serum surface and prevent blood substance exchange between blood cell and serum. dvac Gel and Clot Activator Tubes are used for separation and examination of blood serum. The tubes contain barrier gel that is present in the bottom of the tube. The specific gravity for this material lies between the blood clot and the serum. During centrifugation the barrier gel moves upward to the serum-clot interface, where it forms a stable barrier separating the serum from fibrin and cells, preventing substance exchange between blood cells and serum. As a result, they can keep biochemical character and chemical components of serum unchanged for a long time. Serum can also be aspirated directly from the collection tube, eliminating the need for transfer to another container.