title: Thyroglobulin increment after thyroid hormone withdrawal is a reliable indicator for the detection of significant remnants or metastases in patients with differentiated thyroid carcinoma.
abstract: Serum thyroglobulin (Tg) measurement has a pivotal role in the management of differentiated thyroid carcinoma (DTC). Serum Tg increment after thyroid hormone discontinuation seems to be a better predictor of tumor recurrence, however, minimal Tg increment may not be a specific marker. This study tries to evaluate the importance of different levels of Tg increment after thyroid hormone discontinuation. Fifty-five patients (46 females and 9 males with mean age of 41.40 yrs) with DTC, treated with total or subtotal thyroidectomy and radioiodine-131 ((131)I) were studied. Ninety-one per cent of the patients had papillary carcinoma. Serum Tg and thyroid stimulating hormone (TSH) were measured using high sensitive IRMA assays during thyroxine (T4) suppression and after discontinuation of T4 treatment. The mean time interval between Tg on T4 and off T4 was 110.29+/-53.43 days and less than 180 days in all patients. Serum Tg level was increased >or= 1 ng/ml in 25 patients after discontinuation of T4. Of these patients, 17 had metastatic disease or a detectable thyroid remnant. Of 16 patients with unchanged Tg (-1<DeltaTg<1), 3 had thyroid remnant or metastases. In 14 patients with Tg decrement (Delta<or=-1), 2 patients had a thyroid remnant. The positive predictive value for Tg increment of more than 1, 2 and 5 ng/ml was 68%, 77.2% and 88.9% respectively. All patients with DeltaTg >or= 7 ng/ml had residual disease or metastases. If DeltaTg was unchanged or decreased, the negative predictive value was 83.3%. The sensitivity of WB(131)IS was 63.6% for the detection of thyroid remnant or metastases. Our study indicates that DeltaTg is a more reliable indicator of remnant disease than on T4-Tg or off T4-Tg levels.
authors.affiliation: Department of Nuclear Medicine, Mashad University of Medical Sciences, Mashad, Iran. Zakavi@mums.ac.ir
authors.forename: Rasoul
authors.initials: R
authors.lastname: Zakavi
authors.forename: Zohreh
authors.initials: Z
authors.lastname: Mousavi
authors.forename: Nadir R
authors.initials: NR
authors.lastname: Farid