What is the difference between plasma and serum?

Plasma and serum are both components of blood, but they differ in their composition and how they are obtained. Plasma is the liquid part of blood that is collected when blood is drawn and before it has the chance to clot. It contains clotting factors, including fibrinogen, which are crucial for the blood-clotting process.

In contrast, serum is what remains after blood has clotted. During the clotting process, clotting factors like fibrinogen are used up to form the clot, leaving behind serum, which does not contain these factors. This is why serum is often described as the liquid that separates from the clot after the blood has solidified.

Understanding this distinction is important in laboratory settings, as the choice of whether to use plasma or serum can affect test results, particularly those related to coagulation studies and certain specific tests that may require the presence or absence of clotting factors.