Serum is the clear, liquid component of blood. Serum can be obtained from blood once the blood has been coagulated, or thickened, by clotting.


The clear portion of bodily fluid or blood is known as serum. Serum contains water, proteins, and electrolytes. It does not contain fibrinogen or other clotting factors contained in plasma. Therefore, blood clotting tests can’t be measured using serum. Serum helps with the transportation of certain molecules and hormones throughout the body. Additionally, blood serum can be obtained to measure hormone levels in the body.