What is the composition of serum?

Serum is the clear, yellowish fluid that remains after blood has clotted and the clot has been removed. It is important to note that serum is derived from plasma but lacks clotting factors, such as fibrinogen. When blood clots, these factors are consumed in the formation of the clot, leaving behind the liquid component known as serum. Therefore, the correct characterization of serum is that it is essentially plasma without clotting factors. This makes it distinct from plasma, which contains clotting factors that are important for coagulation and hemostasis.

In contrast, other options provide incorrect descriptions of serum. For example, blood without red blood cells does not accurately represent serum, since serum is derived from the whole blood after clotting, which retains other components including its color, which is largely due to the presence of serum proteins. Additionally, plasma with clotting factors refers specifically to the liquid component of blood that has not undergone clotting and still contains the necessary elements for coagulation. Whole blood without white blood cells would imply that a portion of the blood has been mechanically or chemically treated to remove only the white blood cells, which does not describe the nature of serum accurately. Thus, the definition emphasizing serum as plasma minus clotting factors is