title: [On-levothyroxine measurement of thyroglobulin is not a reliable test for the follow-up of patients at high risk for remnant/recurrent differentiated thyroid carcinoma].
abstract: BACKGROUND
  At present the most widely accepted tool for follow-up management of differentiated thyroid cancer (DTC) patients is serum thyroglobulin (Tg) measurement. It is not uncommon for the serum Tg level to be measured while the patient is taking thyroid hormones (on-treatment Tg measurement). The purpose of the study was to evaluate the accuracy of on-treatment measurement of serum Tg in detecting remnant/recurrent or metastatic disease in high-risk DTC patients.
  
  
  METHODS
  We retrospectively analysed the medical records of 26 high-risk DTC patients and compared the on-treatment and off-treatment Tg levels of these patients. All patients were anti-Tg negative. Using off-treatment measurement of Tg as the gold standard, the results of on-treatment measurement of Tg in the diagnosis of remnant/recurrent disease were analysed for sensitivity, specificity, negative predictive value (NPV) and positive predictive value (PPV).
  
  
  RESULTS
  The median serum Tg level under thyroid hormone suppressive therapy (on-treatment Tg) was 16.5 ng/ml and after withdrawal of thyroid hormone suppressive therapy (off-treatment Tg) was 95.0 ng/ml (P value = 0.001). In 6 patients (23%) the on-treatment Tg level missed the recurrence of the disease. Regarding the off-treatment Tg as the gold standard, the sensitivity, specificity, PPV and NPV of the on-treatment Tg measurement were 72.7%, 100%, 100%, and 40% respectively.
  
  
  CONCLUSIONS
  Normal serum Tg level without TSH-stimulation (on-treatment) is not diagnostically reliable in the follow-up of DTC patients with a high probability of residual/recurrent or metastatic disease.
authors.affiliation: Research Institute for Nuclear Medicine, Shariati Hospital, Medical Sciences/University of Tehran, Tehran, Iran. gholamrezanezhad@razi.tums.ac.ir
authors.forename: Ali
authors.initials: A
authors.lastname: Gholamrezanezhad
authors.forename: Mohsen
authors.initials: M
authors.lastname: Saghari
authors.forename: Sahar
authors.initials: S
authors.lastname: Mirpour
authors.forename: Davood
authors.initials: D
authors.lastname: Beiki
authors.forename: Ali
authors.initials: A
authors.lastname: Tarbiat
authors.forename: Shabnam
authors.initials: S
authors.lastname: Javan
authors.forename: Javaher
authors.initials: J
authors.lastname: Abdollahzadeh
mesh_terms: D000328:Adult; D018931:Antineoplastic Agents, Hormonal / Q000627:therapeutic use; D014408:Biomarkers, Tumor / Q000097:blood*; D018265:Carcinoma, Papillary, Follicular / Q000097:blood / Q000175:diagnosis* / Q000188:drug therapy; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local / Q000097:blood / Q000175:diagnosis*; D018365:Neoplasm, Residual / Q000097:blood / Q000175:diagnosis*; D011237:Predictive Value of Tests; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013954:Thyroglobulin / Q000097:blood*; D013963:Thyroid Hormones / Q000627:therapeutic use; D013964:Thyroid Neoplasms / Q000097:blood / Q000175:diagnosis* / Q000188:drug therapy / Q000556:secondary; D013965:Thyroidectomy; D013974:Thyroxine / Q000627:therapeutic use*
chemical_list: D018931:Antineoplastic Agents, Hormonal; D014408:Biomarkers, Tumor; D013963:Thyroid Hormones; D013954:Thyroglobulin; D013974:Thyroxine