What term describes the fluid portion of blood that contains no red blood cells?

The term that describes the fluid portion of blood without any red blood cells is plasma. Plasma is the liquid component of blood that holds blood cells suspended and constitutes about 55% of total blood volume. It is composed mainly of water (about 90%), electrolytes, proteins, hormones, and waste products, allowing for the transport of these substances throughout the body.

This distinguishes it from serum, which is essentially plasma without the clotting factors like fibrinogen; it is obtained after coagulation has occurred. The buffy coat refers to a thin layer of white blood cells and platelets that sits between the plasma and red blood cells when blood is centrifuged. Platelet-rich plasma is a specific component derived from plasma that is particularly high in platelets and is used in various medical therapies. Thus, plasma is the most correct term to describe the fluid portion of blood without red blood cells.