Plasma that has had its proteins removed is called serum. Serum is a source of electrolytes that is composed of proteins, minerals, carbon dioxide and hormones.
Serum is separated from plasma after blood is donated. After the blood clots, it is placed in a centrifuge. This machine separates the blood and the blood-clotting materials, such as fibrogin and prothrombin, from the red blood cells.
Serum is used to test for many medical conditions. Albumin and globulin, which are serum proteins, are the two components of serum measured to determine some diseases. The liver makes albumin, which can be tested for with a serum albumin test. This test can help diagnose kidney or liver disease.