Importance of the Detection Method for Thyroglobulin Antibodies for the Validity of Thyroglobulin Measurements in Sera from Patients with Graves Disease

Abstract

Abstract Background: The use of recovery tests has been proposed to disclose interferences from anti-thyroglobulin antibodies (TgAbs) in thyroglobulin (Tg) assays. We studied the value of a recovery test in Tg measurement by a new commercial IRMA. Methods: Blood samples were collected from 153 patients with untreated Graves disease. Tg and TgAbs were measured by IRMA and RIA, respectively (Dynotest Tg-plus and Dynotest anti-Tgn; Brahms Diagnostica). The recoveries of added amounts of Tg were calculated for each serum. Results: TgAbs were detected in 72 of the 153 patients (47%). The recovery test results for the 81 TgAb-negative sera (median, 101%; range, 80–115%) were identical to the results for the 91 controls (median, 102%; range, 80–124%). By contrast, significantly lower recovery test results were observed for the 72 TgAb-positive sera (median, 79%; range, 60–103%; Z = −8.363; P <0.0001). In the 34 of the 72 TgAb-positive sera with a normal recovery test, Tg concentrations were significantly lower (median Tg, 13.6 μg/L; range, 1.1–360 μg/L) than those measured in the TgAb-negative sera (median, 107 μg/L; range, 1.2–700 μg/L; Z = −3.797; P <0.0001). Conclusions: Tg values were decreased in TgAb-positive sera even when the results of the recovery tests were normal. This test should not be used alone to determine the validity of a serum Tg measurement in Graves disease.