Undetectable or low (<1 ng/ml) postsurgical thyroglobulin values do not rule out metastases in early stage...

Differentiated thyroid cancer (DTC) work-up is based on (near)total-thyroidectomy plus thyroid remnant ablation (TRA) with 131-radioiodine in many patients, and long-life follow-up. ¹³¹I-post therapy whole body scan (pT-WBS) and serum thyroglobulin (Tg) are used in identifying metastatic patients. Some authors have evaluated the possibility of using post-surgical Tg (ps-Tg) values in deciding for or against TRA. The aim of our study was to verify the diagnostic accuracy of ¹³¹I-pT-WBS and SPECT/CT imaging (post-therapeutic imaging) compared to serum Tg levels in detecting metastases in early stage of DTC patients.

Post-therapeutic imaging revealed metastases in 82 out of 570 (14.4%) patients. Metastases were successively confirmed by other diagnostic tools or by histology (sensitivity and PPV = 100%). Seventy-three out of 82 patients (90.2%) showed ps-Tg levels ≤1 ng/ml. In fifty-four per cent of patients, serum Tg levels at TRA remained ≤1 ng/ml.

In conclusion, ps-Tg levels cannot be used in deciding for or against TRA. In early stage of DTC, post-therapeutic imaging (¹³¹I-pT-WBS and SPECT/CT) is an accurate method of detecting metastases, also in patients with stimulated serum Tg values ≤1 ng/ml.

We retrospectively reviewed the records of 570 consecutive patients affected by pT1-pT3 DTC (F = 450, M = 120), referred to our Nuclear Medicine Units in the last five years to perform TRA after (near)-total-thyroidectomy.All patients underwent TRA 3-4 months after thyroid surgery either in euthyroid or in hypothyroid state. Serum Tg values evaluated in post-surgical period and at TRA were matched with post-therapeutic imaging results.