title: Monitoring thyroglobulin in a sensitive immunoassay has comparable sensitivity to recombinant human tsh-stimulated thyroglobulin in follow-up of thyroid cancer patients.
abstract: BACKGROUND
  Most thyroglobulin (Tg) assays have a sensitivity of 0.5-1 ng/ml. A minority of patients with undetectable T4-suppressed Tg levels have a recombinant human TSH (rhTSH)-stimulated Tg above 2 ng/ml and identifiable residual disease.
  
  
  OBJECTIVE
  The objective was to determine whether a Tg assay with improved sensitivity could eliminate the need for rhTSH stimulation when baseline Tg is below 0.1 ng/ml.
  
  
  METHODS
  A retrospective study of two academic endocrine practices was conducted.
  
  
  METHODS
  A total of 194 patients undergoing rhTSH stimulation participated in the study.
  
  
  RESULTS
  Of the 80 patients with Tg below 0.1 ng/ml, two (2.5%) had rhTSH-stimulated Tg above 2 ng/ml. One other patient with stimulation to 0.3 ng/ml and negative 123I scan had an ultrasound-detected malignant lymph node resected. None had 131I/123I imaging after rhTSH stimulation suggestive of local recurrence or distant metastasis. If T4-suppressed Tg was 0.1-0.5 or 0.6-2.0 ng/ml, rhTSH Tg was above 2 ng/ml in 24.2 and 82.4%, respectively.
  
  
  CONCLUSIONS
  Patients with differentiated thyroid carcinoma and a T4-suppressed serum Tg below 0.1 ng/ml rarely have a rhTSH-stimulated Tg above 2 ng/ml, and none of these patients had 131I or 123I imaging after rhTSH stimulation suggestive of local recurrence or distant metastasis. We recommend monitoring such patients with a T4-suppressed Tg level and periodic neck ultrasonography. An increase in T4-suppressed serum Tg to a detectable level or the appearance of abnormal lymph nodes by physical or ultrasound exam should prompt further investigation.
authors.affiliation: Division of Endocrinology and Metabolism, Mayo Clinic College of Medicine, Jacksonville, Florida 32224, USA. smallridge.robert@mayo.edu
authors.forename: Robert C
authors.initials: RC
authors.lastname: Smallridge
authors.forename: Shon E
authors.initials: SE
authors.lastname: Meek
authors.forename: Melissa A
authors.initials: MA
authors.lastname: Morgan
authors.forename: Geoffrey S
authors.initials: GS
authors.lastname: Gates
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Fox
authors.forename: Stefan
authors.initials: S
authors.lastname: Grebe
authors.forename: Vahab
authors.initials: V
authors.lastname: Fatourechi
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007118:Immunoassay; D008297:Male; D008875:Middle Aged; D011994:Recombinant Proteins / Q000494:pharmacology; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013954:Thyroglobulin / Q000097:blood*; D013964:Thyroid Neoplasms / Q000097:blood*; D013972:Thyrotropin / Q000494:pharmacology*
chemical_list: D011994:Recombinant Proteins; D013972:Thyrotropin; D013954:Thyroglobulin