Serum iron

Serum iron is a medical laboratory test that measures the amount of circulating iron that is bound to transferrin. Clinicians order this laboratory test when they are concerned about iron deficiency, which can cause anemia and other problems.

65% of the iron in the body is bound up in hemoglobin molecules in red blood cells. About 4% is bound up in myoglobin molecules. Around 30% of the iron in the body is stored as ferritin or hemosiderin in the spleen, the bone marrow and the liver. Small amounts of iron can be found in other molecules in cells throughout the body. None of this iron is directly accessible by testing the serum.