title: The diagnostic use of the rhTSH/thyroglobulin test in differentiated thyroid cancer patients with persistent disease and low thyroglobulin levels.
abstract: BACKGROUND
  Serum thyroglobulin (Tg) measurement after TSH stimulation, by either thyroid hormone withdrawal or recombinant human TSH (rhTSH) administration, is the most sensitive method for early detection of patients with persistent or recurrent differentiated thyroid cancer (DTC) after total thyroidectomy and 131I ablation. The use of rhTSH is now increasing because it avoids thyroid hormone suppressive therapy (THST) withdrawal and the consequent symptoms of severe hypothyroidism. Current guidelines suggest measurement of serum Tg 4 days after starting a 2-day course of rhTSH injections, and assumes that Tg reaches maximum serum levels at that time.
  
  
  OBJECTIVE
  The present study was carried out to evaluate the accuracy of rhTSH/thyroglobulin test in DTC patients with persistent disease and low thyroglobulin levels.
  
  
  METHODS
  A series of 13 DTC patients was selected because they had proven persistent disease associated with low Tg levels (< 2.0 micro g/l) under l-thyroxine treatment. In all of them, serum Tg was > 5.0 micro g/l at the last THST withdrawal. We measured serum Tg and TSH levels on days 0.5, 1, 1.5, 2, 4, 7, 10 and 15 after the first of a 2-day course of intramuscular rhTSH injections.
  
  
  RESULTS
  Serum Tg values were variable in terms of both peak and time-course. Detectable serum Tg levels were recorded on day 4 in all patients. However, among these 13 patients, the peak Tg value was reached earlier than day 4 in three patients and later in two others. In one patient, Tg level at day 2 was higher (3.0 micro g/l) than at day 4 (1.8 micro g/l). In six of the 13 patients studied we compared Tg values after rhTSH to those subsequently obtained after THST withdrawal: in five of them Tg values were two to three times higher after the latter stimulation. Serum Tg value variability after rhTSH was partially accounted for by variability of serum TSH levels, which were inversely related to patient body surface.
  
  
  CONCLUSIONS
  In DTC patients with persistent disease and low Tg levels, optimization of the diagnostic use of Tg measurement after rhTSH may require rhTSH dose adjustment to the patient body surface area and repeated blood sampling, in order to improve diagnostic accuracy. In these patients not even a TSH-stimulated serum Tg cut-off of 2.0 micro g/l on day 4 provides 100% accuracy, whereas a cut-off of 1.0 micro g/l seems more appropriate. Therefore, in this subset of patients, if any detectable Tg level >or= 1.0 micro g/l is found after rhTSH, re-evaluation after THST should be advised.
authors.affiliation: Dipartimento di Medicina Interna e Medicina Specialistica, University of Catania Medical School, Catania, Italy.
authors.forename: Gabriella
authors.initials: G
authors.lastname: Pellegriti
authors.forename: Claudia
authors.initials: C
authors.lastname: Scollo
authors.forename: Concetto
authors.initials: C
authors.lastname: Regalbuto
authors.forename: Marco
authors.initials: M
authors.lastname: Attard
authors.forename: Paola
authors.initials: P
authors.lastname: Marozzi
authors.forename: Francesco
authors.initials: F
authors.lastname: Vermiglio
authors.forename: Maria Antonella
authors.initials: MA
authors.lastname: Violi
authors.forename: Michelangela
authors.initials: M
authors.lastname: Cianci
authors.forename: Riccardo
authors.initials: R
authors.lastname: Vigneri
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Pezzino
authors.forename: Sebastiano
authors.initials: S
authors.lastname: Squatrito
mesh_terms: D000328:Adult; D014408:Biomarkers, Tumor / Q000097:blood*; D002291:Carcinoma, Papillary / Q000097:blood / Q000175:diagnosis* / Q000628:therapy; D018265:Carcinoma, Papillary, Follicular / Q000097:blood / Q000175:diagnosis* / Q000628:therapy; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018365:Neoplasm, Residual; D011994:Recombinant Proteins / Q000097:blood; D013954:Thyroglobulin / Q000097:blood*; D013960:Thyroid Function Tests / Q000379:methods; D013963:Thyroid Hormones / Q000627:therapeutic use; D013964:Thyroid Neoplasms / Q000097:blood / Q000175:diagnosis* / Q000628:therapy; D013965:Thyroidectomy; D013972:Thyrotropin / Q000097:blood; D014915:Whole-Body Counting
chemical_list: D014408:Biomarkers, Tumor; D011994:Recombinant Proteins; D013963:Thyroid Hormones; D013972:Thyrotropin; D013954:Thyroglobulin