Serum
Blood serum describes the liquid portion of blood that separates from the blood clot after clotting is complete. Research Donors uses the off-the-clot method for serum samples, in which whole blood is collected, centrifuged at room temperature after clotting is complete, and the serum supernatant is collected. Blood serum contains a broad spectrum of proteins minus clotting factors, as well as nutrients, electrolytes, and metabolites, and is therefore often used for studies of enzyme activity or hormone levels.