What is the fluid portion of the blood called?

The fluid portion of the blood is known as plasma. Plasma is a yellowish liquid that makes up about 55% of total blood volume and contains water, electrolytes, proteins, hormones, nutrients, and waste products. It plays a crucial role in transporting cells, nutrients, and waste throughout the body and maintaining blood pressure and volume.

Serum is often confused with plasma; however, serum is the portion of blood that remains after clotting has occurred and does not contain clotting factors such as fibrinogen. Hemoglobin is a protein found within red blood cells that is responsible for transporting oxygen, but it is not the fluid portion of blood. Albumin is one of the proteins found in plasma, which helps maintain oncotic pressure and transport substances, but it is not the fluid component itself.