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 microg/L; range, 1.1-360 microg/L) than those measured in the TgAb-negative sera (median, 107 microg/L; range, 1.2-700 microg/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.