title: Thyroglobulin levels and thyroglobulin doubling time independently predict a positive 18F-FDG PET/CT scan in patients with biochemical recurrence of differentiated thyroid carcinoma.
abstract: OBJECTIVE
  To assess the relationship between serum thyroglobulin (Tg) levels, Tg doubling time (Tg-DT) and the diagnostic performance of (18)F-FDG PET/CT in detecting recurrences of (131)I-negative differentiated thyroid carcinoma (DTC).
  
  
  METHODS
  Included in the present study were 102 patients with DTC. All patients were treated by thyroid ablation (e.g. thyroidectomy and (131)I), and underwent (18)F-FDG PET/CT due to detectable Tg levels and negative conventional imaging. Consecutive serum Tg measurements performed before the (18)F-FDG PET/CT examination were used for Tg-DT calculation. The (18)F-FDG PET/CT results were assessed as true or false after histological and/or clinical follow-up.
  
  
  RESULTS
  Serum Tg levels were higher in patients with a positive (18)F-FDG PET/CT scan (median 6.7 ng/mL, range 0.7-73.6 ng/mL) than in patients with a negative scan (median 1.8 ng/mL, range 0.5-4.9 ng/mL; P < 0.001). In 43 (88 %) of 49 patients with a true-positive (18)F-FDG PET/CT scan, the Tg levels were >5.5 ng/mL, and in 31 (74 %) of 42 patients with a true-negative (18)F-FDG PET/CT scan, the Tg levels were ≤5.5 ng/mL. A Tg-DT of <1 year was found in 46 of 49 patients (94 %) with a true-positive (18)F-FDG PET/CT scan, and 40 of 42 patients (95 %) with a true-negative scan had a stable or increased Tg-DT. Moreover, combining Tg levels and Tg-DT as selection criteria correctly distinguished between patients with a positive and a negative scan (P<0.0001).
  
  
  CONCLUSIONS
  The accuracy of (18)F-FDG PET/CT significantly improves when the serum Tg level is above 5.5 ng/mL during levothyroxine treatment or when the Tg-DT is less than 1 year, independent of the absolute value.
authors: Department of Nuclear Medicine and Thyroid Centre, Oncology Institute of Southern Switzerland, Bellinzona, Switzerland. luca.giovanella@eoc.ch
authors: Luca
authors: L
authors: Giovanella
authors: Pierpaolo
authors: P
authors: Trimboli
authors: Frederik A
authors: FA
authors: Verburg
authors: Giorgio
authors: G
authors: Treglia
authors: Arnoldo
authors: A
authors: Piccardo
authors: Luca
authors: L
authors: Foppiani
authors: Luca
authors: L
authors: Ceriani
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D003362:Cost-Benefit Analysis; D005260:Female; D019788:Fluorodeoxyglucose F18 / Q000494:pharmacology*; D005500:Follow-Up Studies; D006801:Humans; D007457:Iodine Radioisotopes / Q000494:pharmacology; D008175:Lung Neoplasms / Q000473:pathology; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging; D009362:Neoplasm Metastasis; D011237:Predictive Value of Tests; D019275:Radiopharmaceuticals / Q000494:pharmacology; D012008:Recurrence; D012680:Sensitivity and Specificity; D013954:Thyroglobulin / Q000378:metabolism*; D013964:Thyroid Neoplasms / Q000473:pathology*; D013974:Thyroxine / Q000494:pharmacology; D013997:Time Factors
chemical_list: D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18; D013954:Thyroglobulin; D013974:Thyroxine