Detection of thyroglobulin in antithyroglobulin antibody-positive sera by isoelectric focusing.

Circulating antibodies have the potential to interfere with the measurement of thyroglobulin (Tg) in sera of patients. Here, we determined Tg concentration by isoelectric focusing (IEF) on agarose gel using for detection a rabbit antiserum to human Tg termed FLX. Tg was determined in sera of thyroid patients and HIV-infected patients under antiviral therapy. We showed that Tg IEF was not affected by the presence of anti-Tg antibodies (TgAb). Tg concentrations measured by IEF in TgAb-negative sera were in most of the cases, similar to those obtained by IRMA (immunoradiometric assay). However, in 5 of the 96 thyroid patients, and none of the 46 healthy subjects, Tg was undetectable by antiserum FLX and measurable by IRMA. In HIV-infected patients (64 men and 60 women), Tg was not recognized by FLX in 23 men and 9 women and this was related to abnormal CD4. We hypothesize that the decreased binding of FLX to Tg may be the result of conformational change on the Tg molecule, a phenomenon apparently related to immunodeficiency in HIV-infected patients. For thyroid patients, Tg IEF may be very useful for the interpretation of results when Tg measurements by IRMA and automated immunoassays are affected by interferences.