To investigate the potential role of serum thyroglobulin doubling time (TgDT) in predicting 2-deoxy-2-[18F]fluoro-d-glucose ([18F]FDG) PET/CT results in patients affected by differentiated thyroid carcinoma (DTC) who demonstrated a combination of positive Tg but a negative [131I] whole-body scan ([131I]-WBS). The gene discussed is TG; the disease is differentiated thyroid carcinoma.