Transfusion fluids are a type of medical treatment that involves the transfer of blood or blood components from one person to another. The most common transfusion fluid is serum, which is a clear, yellowish liquid that contains antibodies and other proteins. Serum is used to treat a variety of conditions, including anemia, shock, and trauma. It can also be used to replace lost blood volume in patients who have undergone surgery or suffered from a severe injury.