Dual Role of AITD in TgAb-Positive PTC: Delayed Antibody Clearance with Enhanced RAIT Response

Background and Objective Elevated thyroglobulin antibody (TgAb) levels in postoperative management of papillary thyroid carcinoma (PTC) are often attributed to tumor recurrence, while the potential impact of autoimmune thyroid disease (AITD) is overlooked. This study aims to clarify the comprehensive effects of AITD on baseline TgAb levels, antibody normalization kinetics, tumor recurrence/metastasis risk, and therapeutic efficacy of radioactive iodine (RAI) therapy (RAIT) in PTC patients. Methods A retrospective cohort of 287 TgAb-positive ( ≥115 IU/mL) PTC patients who underwent total thyroidectomy and received RAIT with ≥6 months follow-up was enrolled. Based on postoperative pathology and thyroid peroxidase antibody (TPOAb) status, patients were divided into Group A0 (non-AITD, n = 70) and Group A1 (AITD-concurrent, n = 217). Clinicopathological characteristics, RAIT response, and TgAb normalization were compared. Results 75.6% (217/287) of the TgAb-positive PTC patients had concurrent AITD. Group A1 exhibited higher pre-RAIT TgAb levels (680.7 ± 320.6 vs. 480.2 ± 280.5 IU/mL, p = 0.023) and recurrence/metastasis rates (38.7% vs. 25.7%, p = 0.048) than Group A0. No significant differences existed in gender, age, primary tumor size, extrathyroidal extension, multifocality, number of lymph node metastases, Lymph node metastasis rate, extranodal extension, or TNM stage (all p > 0.05). Group A1 required fewer cycles of RAI than Group A0 ( p = 0.042), though total RAI dose given and final therapeutic response showed no statistical difference (all p > 0.05). The median TgAb normalization time was significantly longer in Group A1 (40.81 months vs. 33.55 months, Log-rank p = 0.043), with Cox regression confirming slower normalization in A1 (HR=0.667, 95% CI: 0.452–0.983). Conclusion Elevated postoperative serum TgAb levels in PTC patients are frequently associated with concurrent AITD, which correlates with higher TgAb levels and increased recurrence/metastasis risk but does not compromise RAIT efficacy. This highlights the dual role of AITD in PTC prognosis: delaying antibody clearance while enhancing treatment responsiveness.