Value of diagnostic radioiodine scintigraphy and thyroglobulin measurements after rhTSH injection

Summary

Measurements 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.

Zusammenfassung

Die Messung von Thyreoglobulin (Tg) im Follow-up von Patienten mit differenzierten Schilddrüsenkarzinomen (DTC) sollte laut Hersteller 72 Stunden nach Verabreichung von rekombinantem humanem Thyrotropin (rhTSH) erfolgen. In unserer Abteilung erfolgen Tg-Messungen 24 und 72 h nach rhTSH-Gabe zusammen mit einer 72h-post-rhTSH ¹³¹I Ganzkörperszintigraphie (GKS). Ziel dieser Studie ist der Vergleich des diagnostischen Nutzens der Tg-Messungen 24 und 72 h nach rhTSH und ¹³¹I-GKS. Patienten und Methoden: 181 Patienten, die in unsere nuklearmedizinische Abteilung zum Follow-up nach ¹³¹I Ablation von DTC überwiesen worden waren, nahmen an dieser Studie teil. In allen Patienten wurden Tg-Messungen 24 h (Tg24) und 72 h (Tg72) nach rhTSH und ¹³¹I-GKS durchgeführt. Die untere Nachweisgrenze der Tg-Bestimmung war 0,2 μg/l. Ergebnisse: 47 Patienten (26%) hatten nachweisbare Tg-Werte: in 4/47 Fällen (8%) war nur Tg24 nachweisbar (immer <1 μg/l), und in 6/47 Fällen (11%), war nur Tg72 nachweisbar. In 10/47 Patienten mit nachweisbaren Tg-Werten waren Tg24 und Tg72 gleichwertig. In 27/47 Fällen war Tg24 niedriger, in 10/47 höher als Tg72. Zwei Patienten mit einem oder zwei positiven Tg-Testergebnissen zeigten auch eine positive ¹³¹I GKS. In 8 Patienten (14%) war nur die ¹³¹I GKS-positiv; ein anatomisches Korrelat für eine solche Tg-Negative, positive GKS wurde in nur 2 Patienten gefunden. Schlussfolgerung: Tg-Messung 72 Stunden nach Injektion von rhTSH zeigt alle klinisch relevanten, nachweisbaren Tg-Werte. Auf diagnostische ¹³¹I Ganzkörperszintigraphie kann verzichtet werden, auch bei Patienten mit hohem Risiko.

Keywords

Thyroglobulin - differentiated thyroid carcinoma - rhTSH

Schlüsselwörter

Thyreoglobulin - differenziertes Schilddrüsenkarzinom, rhTSH

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