Are there disadvantages in administering 131I ablation therapy in patients with differentiated thyroid carcinoma without a preablative diagnostic 131I whole-body scan?

Summary objective To evaluate the risk of performing inappropriate 131I ablative therapies for thyroid carcinoma in patients lacking thyroid remnants or metastases, using a strategy of treatment without a preliminary iodine‐131 diagnostic whole‐body scan (DxWBS). design Retrospective evaluation of post‐therapy whole‐body scans to assess the prevalence of thyroid remnants or metastases after total thyroidectomy. Comparison of 131I uptake test and thyroglobulin (Tg) off levothyroxine (L‐T4) performed before therapy with post‐therapy scans, in order to evaluate the ability to predict inappropriate treatments. patients A group of 875 consecutive patients with previous total or near‐total thyroidectomy for differentiated thyroid carcinoma underwent 131I ablative therapy without a preliminary 131I‐DxWBS. All patients were clinically free of distant metastases and macroscopic residual tumour. measurements Whole‐body scans were performed 2–5 days after the treatment as gold standard for thyroid remnants and metastases; 24‐h 131I quantitative neck uptake test and Tg off L‐T4 were performed before 131I therapy. results The majority of patients (94%) were found to have thyroid remnants or metastases at post‐therapy scans, in most cases (91·2%) with detectable Tg off L‐T4 and positive 24‐h neck uptake. 14 patients (1·6%) with tiny lymph‐node metastases positive at post‐therapy scans showed undetectable Tg off L‐T4. In 30 patients (3·6%) faint positive post‐therapy images for thyroid remnants have been classified as false‐positive results on the basis of both negative 24‐h neck uptake and undetectable Tg off L‐T4. conclusions This study confirms that most patients have residual thyroid tissue after total thyroidectomy and that it seems reasonable to omit routine diagnostic whole‐body scans before 131I treatment with clinical, managerial and economic advantages.