Transferrin receptor in tissue and serum: updated clinical significance of soluble receptor.

The transferrin receptor is an essential component of cellular uptake of iron, and it binds to serum transferrin. Recently, 2 different types of transferrin receptors have been recognized: transferrin receptor (TfR or transferrin receptor 1) and transferrin receptor 2. Most cells possess a ubiquitous system controlling the biosynthesis of TfR at the posttranscriptional level to avoid excess iron influx into the cells through TfR. During the process of recycling of transferrin receptors, some are shed and appear as soluble or serum transferrin receptors. Measurement of serum transferrin receptor is a new marker of iron metabolism that reflects body iron stores and total erythropoiesis. It has been shown that serum transferrin receptor to ferritin ratios have significant predictive value for differentiating iron deficiency anemia from non-iron deficiency anemia, such as anemia of chronic disorders, whereas serum ferritin is the only significant independent predictor of iron deficiency anemia.