A special coating on the internal wall of the tubes containing microscopic silica particles activates clotting.
VACUETTE®
Z Serum Sep Clot Activator tubes contain an inert separator gel on the
base of the tube which, after centrifugation, forms a stable barrier
between the serum and the blood clot. VACUETTE® Z Serum Sep Clot Activator tubes improve the serum yield and allow samples to be stored in primary tubes.