What is the main difference between serum and plasma?

The distinction between serum and plasma is significant in both clinical and laboratory settings. Plasma is the liquid component of blood that contains water, electrolytes, nutrients, hormones, proteins, and waste products. Crucially, it contains clotting factors, including fibrinogen, which plays a vital role in blood coagulation.

On the other hand, serum is derived from plasma once it has clotted. When blood is allowed to clot, fibrinogen is converted to fibrin, which helps in the formation of a clot. As a result, the liquid that remains after this clotting process—serum—does not contain fibrinogen or any other clotting factors.

Therefore, the correct answer highlights that plasma contains fibrinogen, while serum does not, illustrating a fundamental difference between these two components of blood. Understanding this difference is crucial in various applications, such as laboratory diagnostics, where the choice between serum and plasma can affect the results of certain tests.