There are several parameters in use to estimate total body iron stores in the diagnosis of iron deficiency and iron deficiency anemia. Serum iron represents only a minor fraction of total body iron and is subject to major fluctuations due to influx or efflux from tissue iron stores. In addition, it shows a great diurnal variability, and is therefore a very poor parameter of iron deficiency. Iron saturation of its transporter protein in blood, transferrin, is similarly difficult to interpret, as it depends also in part on the determination of serum iron levels. Ferritin, the tissue iron storage protein, is released into the circulation during active liver cell damage, and, quite unlike serum transferrin levels, ferritin levels rise during the acute phase response of the inflammatory reaction. In most cases, however, the serum ferritin level, if substantiated by the concurrent determination of the C-reactive protein and the alanine-leucine-aminotransferase (ALT) to exclude both, occult liver cell damage and inflammation, correlates well with total body iron stores and total body iron deficiency, respectively.