Iron test is a laboratory test that are done to evaluate the iron level in blood serum. Iron is an essential trace element; it is necessary for the formation of red blood cells and certain enzymes. At the other extreme, high levels of iron can be poisonous. Serum iron levels show a marked diurnal variation with morning levels higher by 30%. They are also rapidly depressed to low levels by acute or chronic infections or any other chronic disorder. Because of these large fluctuations, serum iron is of little diagnostic use on its own but when combined with iron–binding capacity/transferrin and ferritin, total body iron deficiency or excess can usually be defined.