title: Undetectable thyroglobulin in patients with differentiated thyroid carcinoma and residual radioiodine uptake on a postablation whole-body scan.
abstract: OBJECTIVE
  To assess the impact of laboratory interferences and pitfalls in producing falsely undetectable Tg in differentiated thyroid carcinoma (DTC) patients with residual iodine-avid thyroid tissue on a posttreatment whole-body scan (PT-WBS).
  
  
  METHODS
  From 298 consecutive patients with histologically proven DTC, 47 patients (16%) with undetectable serum Tg but residual ¹³¹I uptake on a PT-WBS were selected. Interferences from antithyroglobulin antibodies (TgAb), heterophile antibodies, and hook-effects were screened; in the remaining samples, serum Tg was measured in 3 different immunoassays.
  
  
  RESULTS
  Of 47 patients, 11 (23%) showed interference from either thyroglobulin antibodies (n = 10) or heterophile antibodies (n = 1). Among the 36 remaining patients, 18 showed detectable Tg levels after retesting using a different immunoassay, whereas the remaining 18 patients also showed detectable Tg levels in a third Tg immunoassay. However, only 7 patients showed a detectable Tg in both secondarily used assays. Tg levels remained undetectable in all methods in 9 patients (19%) even after extensive laboratory work-up and despite the presence of ¹³¹I-avid tissue found in PT-WBS.
  
  
  CONCLUSIONS
  A careful assessment of interferences in Tg measurement significantly reduced the occurrence of undetectable Tg among patients with ¹³¹I uptake in PT-WBS. However, such extensive assessment is difficult in clinical practice and one-fifth of patients still had undetectable Tg in multiple assays despite an intensive laboratory work-up. A benchmark between ¹³¹I imaging and Tg measurement authenticates the interpretation of Tg measurements and, consequently, remains of pivotal value by authenticating the use of serum Tg during further follow-up of DTC patients.
authors.affiliation: Department of Nuclear Medicine and Thyroid Centre, Oncology Institute of Southern Switzerland, Bellinzona, Switzerland. luca.giovanella@eoc.ch
authors.forename: Luca
authors.initials: L
authors.lastname: Giovanella
authors.forename: Sergio
authors.initials: S
authors.lastname: Suriano
authors.forename: Luca
authors.initials: L
authors.lastname: Ceriani
authors.forename: Frederik Anton
authors.initials: FA
authors.lastname: Verburg
mesh_terms: D055011:Ablation Techniques; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001692:Biological Transport; D002454:Cell Differentiation; D005188:False Negative Reactions; D005260:Female; D006801:Humans; D007118:Immunoassay; D007457:Iodine Radioisotopes / Q000378:metabolism / Q000627:therapeutic use; D008297:Male; D008875:Middle Aged; D013954:Thyroglobulin / Q000276:immunology / Q000378:metabolism*; D013964:Thyroid Neoplasms / Q000175:diagnosis* / Q000378:metabolism* / Q000473:pathology / Q000601:surgery; D051598:Whole Body Imaging; D055815:Young Adult
chemical_list: D007457:Iodine Radioisotopes; D013954:Thyroglobulin