title: Ablative free thyroxine to thyroglobulin ratio as a predictor of differentiated thyroid cancer recurrence.
abstract: BACKGROUND
  Serum thyroglobulin (Tg), a widely used thyroid cancer marker, is limited at the time of ablation, unable to differentiate between diseased and normal residual tissue.
  
  
  OBJECTIVE
  We evaluated the use of the ablation free thyroxine to thyroglobulin ratio (fT4:Tg) as a tumour-specific ratio for predicting persistence or recurrence in differentiated thyroid cancer.
  
  
  METHODS
  Retrospective chart review.
  
  
  METHODS
  McGill University Health Centre.
  
  
  METHODS
  Of 234 patients, 84 were analyzed after exclusion of those with anti-Tg antibodies, ablation Tg < or = 2, and follow-up < 3 months. Ablation thyroxine and Tg levels were recorded and patients were followed to detect recurrence. The relationship between the ablation fT4:thyroglobulin ratio and recurrence was evaluated.
  
  
  METHODS
  Hazards ratio (HR) for predictive fT4:Tg ratio cutoff value and disease-free survival based on the fT4:Tg ratio.
  
  
  RESULTS
  Thirty-eight percent of patients developed recurrence: 8 pathologically proven and 24 suspected. Eighty-one percent of patients with recurrence had an fT4:Tg < 27%, in contrast to 23% of those without recurrence (HR 6.2; p < .001). Of all patients with fT4:Tg < 27%, 68% developed evidence of recurrence compared with 13% with fT4:Tg > or = 27% (p < .001). Recurrences in the fT4:Tg < 27% group occurred twice as early.
  
  
  CONCLUSIONS
  Ablation fT4:Tg < 27% is predictive of recurrence and should be used to identify high-risk patients.
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, University of Sherbrooke, Sherbrooke, Quebec, Canada.
authors.forename: Margaret
authors.initials: M
authors.lastname: Aron
authors.forename: Valerie
authors.initials: V
authors.lastname: Cote
authors.forename: Michael
authors.initials: M
authors.lastname: Tamilia
authors.forename: Michael
authors.initials: M
authors.lastname: Hier
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Black
authors.forename: Xun
authors.initials: X
authors.lastname: Zhang
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Payne
mesh_terms: D000328:Adult; D000368:Aged; D014408:Biomarkers, Tumor / Q000097:blood*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local / Q000175:diagnosis*; D012189:Retrospective Studies; D013954:Thyroglobulin / Q000097:blood*; D013964:Thyroid Neoplasms / Q000097:blood / Q000175:diagnosis* / Q000532:radiotherapy / Q000601:surgery; D013974:Thyroxine / Q000097:blood*; D055815:Young Adult
chemical_list: D014408:Biomarkers, Tumor; D013954:Thyroglobulin; D013974:Thyroxine