Sensitive assay for thyroglobulin autoantibodies in serum employing polyethylene glycol for precipitation

Abstract

A sensitive assay for thyroglobulin autoantibodies (Tg-ab) is described. The assay is based on prolonged incubation of [¹²⁵I]Tg with serum followed by precipitation of antibody bound [¹²⁵I]Tg by polyethylene glycol (PEG). The PEG concentration was chosen to give a low precipitation of free [¹²⁵I]Tg while effectively precipitating Tg-ab-bound [¹²⁵I]Tg. The lowest reference employed contained 19.5 MRC U/l Tg-ab. This was always different from an incubate without Tg-ab. Tg standard added to samples interfered in the assay giving spuriously low Tg-ab values as in other Tg-ab assays. Tg-ab added to samples was recovered quantitatively. The interassay coefficient of variation was 19.8% and the intra-assay coefficient of variation 11.3%. Only eight of 66 serum samples with various amounts of Tg-ab, measured with the new assay, had levels of Tg-ab detectable by the passive haemagglutination test.

Key Words:

• autoimmunity
• thyroid disease