Thyroglobulin antibody (TgAb) is a known source of analytical interference in the measurement of serum thyroglobulin (Tg), a key biochemical marker used for monitoring differentiated thyroid carcinoma (DTC). In patients with positive TgAb, Tg concentrations may appear falsely low, reducing the reliability of Tg as a marker of disease status. Consequently, TgAb levels and their trends have been proposed as surrogate indicators of residual or metastatic disease. This study aimed to compare TgAb levels between metastatic and non-metastatic DTC patients and to identify an optimal TgAb cutoff value for predicting metastatic involvement following initial therapy.

This retrospective observational study included 41 patients with histologically confirmed DTC treated at Dr. Hasan Sadikin General Hospital Bandung. All patients underwent total thyroidectomy followed by initial RAI-131 ablation and were reassessed 6 to 9 months after therapy between May and November 2025. The cohort consisted of 29 female and 12 male patients. Based on post-treatment clinical evaluation and imaging findings, patients were classified into a non-metastatic group (n = 27) and a metastatic group (n = 14). TgAb levels measured at follow-up were compared between the two groups. Receiver operating characteristic (ROC) curve analysis was performed to determine the TgAb cutoff value with the highest diagnostic accuracy for predicting metastasis.

Patients in the metastatic group exhibited significantly higher TgAb levels than those in the non-metastatic group (p = 0.001). ROC analysis demonstrated an optimal TgAb cutoff value of 48.4 IU/mL, with an AUC of 0.856, indicating robust diagnostic differentiation. At this threshold, the sensitivity for predicting metastatic disease was 71.4%, while specificity reached 88.9%, suggesting substantial clinical utility for identifying patients at increased risk of metastatic involvement.

Elevated TgAb levels are strongly associated with metastatic DTC after initial therapy. A TgAb threshold of 48.4 IU/mL provides high diagnostic accuracy and may serve as an effective surrogate marker in patients where Tg measurement is unreliable due to antibody interference. Incorporation of TgAb-based risk assessment into routine follow-up may enhance early detection of metastatic disease. Prospective validation in larger cohorts is recommended.