Value of diagnostic radioiodine scintigraphy and thyroglobulin measurements after rhTSH injection

Abstract

SummaryMeasurements of thyroglobulin (Tg) levels 72 h after administration of recombinant human thyrotropin (rhTSH) are recommended by the manufacturer in the follow-up of patients with differentiated thyroid carcinoma (DTC). In our department, Tg measurements are performed both 24 h and 72 h after administration of rhTSH, together with 72 h post rhTSH 131I whole body scintigraphy (WBS). The objective of this study is to compare the diagnostic usefulness of Tg measurements 24 and 72 h after rhTSH administration, and 131I WBS. Patients and methods: 181 patients were included who had been referred to our Nuclear Medicine Department for follow-up after 131I ablation of DTC. Tg measurements 24 h (Tg24) and 72 h (Tg72) after rhTSH, and 131I WBS, were done in all patients. The lower detection limit of Tg was 0,2 μg/l. Results: 47 patients (26%) had detectable Tg levels: in 4/47 cases (8%) only Tg24 was detectable (always <1 μg/l), and in 6/47 cases (11%), only Tg72 was detectable. In 10/47 patients with detectable Tg-levels, Tg24 and Tg72 tested equally. In 27/47 cases, Tg24 was lower, and in 10/47 higher, than Tg72. Two patients with one or two positive Tg-test results also had a positive 131I WBS. In 8 patients (14%) only the 131I WBS was positive; an anatomical substrate for such a Tgnegative positive WBS was confirmed in only 2 patients. Conclusion: Tg-measurement 72 hours after rhTSH injection reveals all clinically relevant detectable Tg-levels. Diagnostic 131I scintigraphy may be omitted, even in highrisk patients.

The Role of Routine Diagnostic Radioiodine Whole-Body Scintigraphy in Patients with High-Risk Differentiated Thyroid Cancer

“…Only the study by Verburg et al analyzed high-risk patients separately, but the high-risk group contained only 44 patients and lacked a clear formulation of high-risk criteria. Still, the authors concluded that routine DxWBS might be omitted in high-risk patients just as in low-risk patients (12). Other studies have found that in their study population, which also included high-risk patients, DxWBS had no value additional to that provided by stimulated thyroglobulin measurement (12)(13)(14)(15)(16)(17).…”

Utility of Diagnostic Whole-Body Iodine Scanning in High-Risk Differentiated Thyroid Carcinoma

“…However, the original phase III clinical trial comparing rhTSH and THW preparation for DxWBS concluded that rhTSH DxWBS was less sensitive than DxWBS using THW (7). In this phase III trial, rhTSH DxWBS was inferior to THW DxWBS in 18 (29%) of 62 patients and failed to detect metastatic disease in 8 (13%) of 62 patients with positive scans.…”

“…Several studies analyzed the additional value of DxWBS, but also in low-risk patients (3)(4)(5)(6)(7)(8)(9)(10). Most studies found no additional value of DxWBS in their patient group (3-9).…”

Reply: Utility of Diagnostic Whole-Body Iodine Scanning in High-Risk Differentiated Thyroid Carcinoma

“…Several studies analyzed the additional value of DxWBS, but also in low-risk patients (3)(4)(5)(6)(7)(8)(9)(10). Most studies found no additional value of DxWBS in their patient group (3)(4)(5)(6)(7)(8)(9).…”