Electronic Letters to:

Endocrine Care: Robert C. Smallridge, Shon E. Meek, Melissa A. Morgan, Geoffrey S. Gates, Thomas P. Fox, Stefan Grebe, and Vahab Fatourechi Monitoring Thyroglobulin in a Sensitive Immunoassay Has Comparable Sensitivity to Recombinant Human TSH-Stimulated Thyroglobulin in Follow-Up of Thyroid Cancer Patients J Clin Endocrinol Metab 2007; 92: 82-87 [Abstract] [Full text] [PDF]

eLetters: Submit a response to this article

Electronic letters published:

Is Slightly Detectable rhTSH-Tg Clinically Relevant when Undetectable onT4-Tg occured?

Luca Giovanella   (13 November 2006)

Is Slightly Detectable rhTSH-Tg Clinically Relevant when Undetectable onT4-Tg occured? 13 November 2006
Luca Giovanella, chief, nuclear medicine/thyroid unit ente ospedaliero cantonale, CH6500 Bellinzona, Switzerland Send letter to journal: Re: Is Slightly Detectable rhTSH-Tg Clinically Relevant when Undetectable onT4-Tg occured? luca.giovanella{at}eoc.ch Luca Giovanella	Recently Smallridge and co-workers (1) demonstrated that rhTSH stimulation may be safely omitted when an undetectable (<0.1 ng/ml) thyroglobulin is detected by high-sensitive assay during T4 treatment. These results are in agreement with our previously reported data, obtained with a different Tg immunoassay (2). However, a higher proportion of patients (31 out of 79; 39%) with no evidence of disease and undetectable Tg on T4, but slightly detectable rhTSH-stimulated Tg (i.e., from 0.1 to 2 ng/ml) was reported in the Smallridge’s series than ours, in which only 4 of 103 (4%) patients without evident disease showed a change from undetectable to detectable Tg after rhTSH stimulation, with Tg values ranging from 0.4 to 1.4 ng/ml (data not previously shown). We employed a fixed 3.7 GBq ablative radioiodine activity whereas some patients in the Smallridge’s series received lower radioiodine activity (i.e. 1.1 GBq). Consequently, persistence of small thyroid remnants after low-dose ablation should be considered as a possible explanation for the difference between study findings. From the clinical point-of-view, these observations do not lessen the impact of Smallridge’s results. As we have both demonstrated, a slight rhTSH-stimulated increase in Tg is generally not clinically importance when Tg on T4 is undetectable by immunoassay with high-functional sensitivity (2, 3). We suggest a further analysis of patients with slightly detectable rhTSH-stimulated Tg values to assess the relationship between thyroid remnants and stimulated Tg levels. References 1. Smallridge RC, Meek SH, Morgan MA, Gates GS, Fox TP, Grebe S, Fatourechi V. 2006. Monitoring thyroglobulin in a sensitive immunoassays has comparable sensitivity to recombinant human TSH stimulatied thyroglobulin in follow-up of thyroid cancer patients. J Clin Endocrinol Metab (epub ahead of print October 31, 2006) 2. Giovanella L, Ceriani L, Ghelfo A, Keller F, Sacchi A, Maffioli M, Spriano G. 2006. Thyroglobulin assay during thyroxine treatment in low-risk differentiated thyroid cancer management: comparison with recombinant human thyrotropin-stimulated assay and imaging procedures. Clin Chem Lab Med 44:248-252 3. Kloos RT, Mazzaferri E. 2005. A single recombinant human thyrotropin-stimulated serum thyroglobulin measurements predicts differentiated thyroid carcinoma metastases three to five years later. J Clin Endocrinol Metab 90:5047-5057