Abstract
We investigated the analytical interference of antithyroglobulin antibody (TgAb) to thyroglobulin (Tg) measurement and tried to convert measured Tg concentration to true Tg concentration using a mathematical equation which includes a concentration of TgAb. Methods. Tg was measured by immunoradiometric assay and TgAb by radioimmunoassy. Experimental samples were produced by mixing Tg and TgAb standard solutions or mixing patients' serum with high Tg or high TgAb. Mathematical equations for prediction of expected Tg concentration with measured Tg and TgAb concentrations were deduced. The Tg concentration calculated using the equations was compared with the expected Tg concentration. Results. Measured Tg concentrations of samples having high TgAb were significantly lower than their expected Tg concentration. Magnitude of TgAb interference with the Tg assay showed a positive correlation with concentration of TgAb. Mathematical equations for estimation of expected Tg concentration using measured Tg and TgAb concentrations were successfully deduced and the calculated Tg concentration showed excellent correlation with expected Tg concentration. Conclusions. A mathematic equation for estimation of true Tg concentration using measured Tg and TgAb concentration was deduced. Tg concentration calculated by use of the equation might be more valuable than measured Tg concentration in patients with differentiated thyroid cancer.
Highlights
Thyroglobulin (Tg), a glycoprotein synthesized in normal or malignant thyroid follicular cells, is an important marker for residual or recurrent differentiated thyroid cancer
Undetectable Tg is one of the criteria to establish the absence of a persistent tumor or recurrence in patients with differentiated thyroid cancer who have undergone total thyroidectomy and remnant ablation with radioiodine [1, 2]
No the presence of antithyroglobulin antibody (TgAb)-proof Tg assay (Tg assay without influence of TgAb) has been made available, and the presence of TgAb causes the concentration of measured Tg to be lower than that of the true concentration [4,5,6]
Summary
Thyroglobulin (Tg), a glycoprotein synthesized in normal or malignant thyroid follicular cells, is an important marker for residual or recurrent differentiated thyroid cancer. Undetectable Tg is one of the criteria to establish the absence of a persistent tumor or recurrence in patients with differentiated thyroid cancer who have undergone total thyroidectomy and remnant ablation with radioiodine [1, 2]. In patients with differentiated thyroid cancer who underwent curative treatment with total thyroidectomy followed by high-dose radioiodine ablation, the cut off value of Tg for performance of imaging studies for detection of persistent disease or recurrence is variable, according to the status of TSH and the concentration of measured TgAb [1]. 4.7-930.0 18.5-930.0 111.0-930.0 246.0-930.0 for predicting persistent or recurrent disease according to TSH status (stimulated or not stimulated) Another factor to consider in interpretation of measured Tg value is the presence or absence of TgAb, the strongest serologic factor interfering in accuracy of available Tg assays [3, 8]. The authors assessed the influence of TgAb on measurement of Tg and developed a mathematical equation for estimation of true Tg concentration under various concentrations of TgAb using data from experiments that employed both standard solutions of Tg and TgAb measurement kits and patients’ serum having high Tg or high TgAb
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