What is the fluid portion of blood called after clotting has occurred?

The fluid portion of blood that remains after clotting has occurred is known as serum. When blood clots, the clotting factors and cells become part of the clot, leaving behind the clear, straw-colored fluid that is serum. This fluid contains water, electrolytes, proteins (excluding clotting factors), and waste products.

In contrast, plasma, which is often confused with serum, contains clotting factors and is the liquid component of uncoagulated blood. Whole blood refers to blood that contains all of its components, including cells, plasma, and clotting factors, whereas the buffy coat is a thin layer that contains white blood cells and platelets but is not a fluid component. Understanding these distinctions is crucial for applications in laboratory practice, particularly when interpreting results of lab tests that utilize these different components of blood.