title: Serum thyroglobulin measurements in thyroid cancer: evaluation of 'false' positive results.
abstract: OBJECTIVE
  Serum thyroglobulin (Tg) should be undetectable in patients successfully treated for thyroid carcinoma. We have examined the course of disease in 19 patients with raised serum Tg (greater than 5 micrograms/l) on initial measurement but no other evidence of residual, recurrent or metastatic cancer.
  
  
  METHODS
  416 patients from several centres were followed for periods between 1 and 9 years. Serum Tg was measured at 6-12-month intervals.
  
  
  METHODS
  All had differentiated thyroid cancer, treated by partial or total thyroidectomy and/or 131I ablation, and were receiving suppressive thyroxine therapy.
  
  
  METHODS
  Serum Tg was measured and clinical, X-ray and scan assessment made of presence or absence of residual, recurrent or metastatic cancer.
  
  
  RESULTS
  Of 416 patients initially assessed, only 19 had Tg greater than 5 micrograms/l but no clinical or radiological evidence of disease. At follow-up, 11 patients had developed overt signs of malignancy; one had been treated with 131I with a subsequent fall in Tg; five had Tg between 5 and 20 micrograms/l with incompletely suppressed TSH levels; two subjects remained with slightly elevated Tg and undetectable TSH.
  
  
  CONCLUSIONS
  Patients with elevated Tg require careful follow-up even in the apparent absence of disease. Moderate elevation of serum Tg may be due to inadequate thyroxine suppression therapy, assessed by detectable TSH values measured in a sensitive assay.
authors.affiliation: Department of Medicine, University of Birmingham, Queen Elizabeth Hospital, UK.
authors.forename: E G
authors.initials: EG
authors.lastname: Black
authors.forename: M C
authors.initials: MC
authors.lastname: Sheppard
mesh_terms: D014408:Biomarkers, Tumor / Q000097:blood*; D005189:False Positive Reactions; D005500:Follow-Up Studies; D006801:Humans; D013954:Thyroglobulin / Q000097:blood*; D013964:Thyroid Neoplasms / Q000097:blood* / Q000532:radiotherapy / Q000601:surgery; D013965:Thyroidectomy; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000627:therapeutic use
chemical_list: D014408:Biomarkers, Tumor; D013972:Thyrotropin; D013954:Thyroglobulin; D013974:Thyroxine