Long-term predictive value of highly sensitive thyroglobulin measurement.

Abstract

To examine the predictive value of unremarkable nonstimulated highly sensitive thyroglobulin (hsTg) measurement with regard to the results of stimulated thyroglobulin (Tg) measurement,diagnostic whole-body scintigraphy,recurrenceand differentiated thyroid cancer(DTC)-related death. We retrospectively analysed the data of all 461 (410 without anti-Tg-antibodies [TgAbs], 51 with)DTCpatients who were referred to our department for treatment and follow-up care of differentiated thyroid cancer from 2004 onwards, and in whom at least one posttreatment Tg value was measured in our hospital at least 3 months after I-131 ablation. In the group of TgAb-negative patients, 2.0% of patients with an unstimulated Tg < 0.1 ng/ml showed a stimulated Tg ≥ 1.0 ng/ml, whereas this happened in 77.6% with an unstimulated Tg ≥ 0.1 but <1.0 ng/ml. An unstimulated hsTg ≥ 0.1 ng/ml had a sensitivityspecificitypositive and negative predictive value of 90.0%, 94.1%, 77.6%and 97.6%, respectively, for a stimulated Tg ≥ 1.0 ng/ml. In TgAb-positive patients, this was 75%, 97%, 75%and 97%, respectively. An unstimulated Tg ≥ 0.1 ng/ml did not significantly discriminate with regard to the risk of DTC-related death (p = .06), but ≥1.0 ng/ml did (p = .012), as did a stimulated Tg ≥ 1.0 ng/ml (p = .029). Excluding patients with distant metastases at diagnosis nullifies this significance. Except for patients with distant metastases, both TgAb negative and TgAb positive patients with an undetectable nonstimulated hsTg measurement have a very good prognosis. The high net present value of unstimulated hsTg testing means that further diagnostic procedures can be omitted in such patients.