Serum Thyroglobulin Autoantibodies: Prevalence, Influence on Serum Thyroglobulin Measurement, and Prognostic Significance in Patients with Differentiated Thyroid Carcinoma¹

Abstract

The prevalence of circulating thyroid autoantibodies (TgAb or antithyroid peroxidase) was increased nearly 3-fold in patients with differentiated thyroid cancers (DTC) compared with the general population (40% vs. 14%, respectively). Serum TgAb (with or without antithyroid peroxidase) was present in 25% of DTC patients and 10% of the general population. Serial postsurgical serum TgAb and serum Tg patterns correlated with the presence or absence of disease. Measurements of serum Tg were made in 87 TgAb-positive sera by a RIA and two immunometric assay (IMA) methods to study TgAb interference. TgAb interference, defined as a significant intermethod discordance (>41.7% coefficient of variation) between the Tg RIA and Tg IMA values relative to TgAb-negative sera, was found in 69% of the TgAb-positive sera. TgAb interference was characterized by higher Tg RIA vs. IMA values and was, in general, more frequent and severe in sera containing high TgAb concentrations. However, some sera displayed marked interference when serum TgAb was low (1-2 IU/mL), whereas other sera with very high TgAb values (>1000 IU/mL) displayed no interference. An agglutination method was found to be too insensitive to detect low TgAb concentrations (1-10 IU/mL) causing interference. Exogenous Tg recovery tests were an unreliable means for detecting TgAb interference. Specifically, the exogenous Tg recovered varied with the type and amount of Tg added and the duration of incubation employed. Further, recoveries of more than 80% were found for some sera displaying gross serum RIA/IMA discordances. The measurement of serum Tg in DTC patients with circulating TgAb is currently problematic. It is important to use a Tg method that provides measurements that are concordant with tumor status. IMA methods are prone to underestimate serum when TgAb is present, increasing the risk that persistent or metastatic DTC will be missed. The RIA method used in this study provided more clinically appropriate serum Tg values in the group of TgAb-positive patients with metastatic DTC. Furthermore, as serial serum TgAb measurements paralleled serial serum Tg RIA measurements, TgAb concentrations may be an additional clinically useful tumor marker parameter for following TgAb-positive patients. Disparities between serial serum Tg and TgAb measurements might alert the physician to the possibility of TgAb interference with the serum Tg measurement and prompt a more cautious use of such data for clinical decision-making.

Papillary thyroid microcarcinoma

“…АТ-ТГ выявляются приблизительно у 20% паци-ентов с ВДРЩЖ и не влияют на исход заболевания [90][91]. АТ-ТГ взаимодействуют с ТГ в сыворотке при анализе, снижая цифры ТГ при анализе во время наблюдения за этими пациентами.…”

Comperative study of biotin, streptovidin -ELISA and peroxidase - ELISA for the estimation of TSH in thyroid diseases

“…The current widely used immunometric or sandwich assays (second generation) have a functional sensitivity of 0.1 mU/L. Further developments have led to third-generation chemiluminescence assays, with about a ten-fold improvement in functional sensitivity (1). Extremely sensitive TSH assays are now available; the 4th/5th generation assays can detect TSH levels as low as 0≤0.004mU/L.…”

In vitro assays to test the interference of anti-thyroglobulin antibodies on thyroglobulin measurement

“…Even low concentrations of TgAb that may not be detected by some methods can interfere with Tg measurement [14,15]. On the other hand, TgAb are detected in a higher percentage of DTC patients [16] than the general population (25% vs. 10%, respectively) [17,18].…”