How long does it take for red blood cells to clot, so serum can be pipetted?
There is some variation from cow to cow, but usually 1cc of blood will clot in 20 to 30 minutes. Larger columns of blood will require longer times to clot. Clotting is speeded up at the beginning by using a wooden applicator stick or toothpick to rim the sides of the syringe barrel or tube holding the blood.
