Test Details: Iron uptake into cells is mediated through internalizing iron-transferrin complexes. The iron-transferrin complex binds to transferrin receptors present on the external face of the plasma membrane, and is internalized through endosomes with release of iron into the cytoplasm. Soluble transferrin receptors can be tested in the blood for evaluation of suspected iron deficiency in patients who may have inflammation, infection, or chronic disease. The concentration of sTFR is an indicator of iron status.