Polyethylene Glycol Increases the Detection of Anti-Thyrotropin Receptor Antibodies by a Radioreceptor Assay

Autoantibodies to the thyrotropin (TSH) receptor (TSHR) are the hallmark of the autoimmune response to the thyroid gland and are responsible for thyrotoxicosis in Graves disease (1). Unlike other autoantibodies, there is no direct assay for TSHR antibodies. Instead, these antibodies are detected either by their ability to inhibit binding of radiolabeled TSH to receptors or by a bioassay of TSHR activation (2)(3). The most widely used assay is a radioreceptor assay, which uses solubilized porcine TSHR, in which the antibody is called TSH-binding inhibitory immunoglobulin (TBII). Serum TBII is easily assayed with a commercially available kit; however, 5–10% of patients with Graves disease show a negative reaction perhaps related to inadequacies of the assay (4).Addition of polyethylene glycol (PEG) enhances cAMP production induced by a patient’s IgG, but not by TSH, forskolin, or GTPγS in an in vitro bioassay for thyroid stimulators (5), suggesting that the enhancement occurs at the step of antibody-receptor interaction. We recently found …