A test that compares the clearance (for example, the rate that the kidneys excrete and clear the bloodstream) of IgG (an antibody), versus the clearance of transferrin (an iron-transport protein).В The comparison is done using mathematical calculations after immunoelectrophoresis of serum and immunoelectrophoresis of urine. See immunoelectrophoresis - serum and immunoelectrophoresis - urine.