Published studies (randomised controlled trials, systematic reviews, cohort studies, cross-sectional studies, case series) that assessed use of a low-iodine diet in preparation for radioactive iodine treatment or scanning in patients with well-differentiated non-medullary thyroid carcinoma who had undergone thyroidectomy were eligible for inclusion. Eligible interventions were those where an iodine-restricted diet was compared to no such diet or a variation of the diet. Both internal and external controls were considered; further details reported in the paper.
The primary outcome measure was efficacy of remnant ablation or elimination of any residual cancer or a stimulated thyroglobulin measurement less than 2ug/L or a combination. Secondary outcomes were urinary iodine measurements, radioactive iodine kinetics and long-term thyroid cancer outcomes.
All the included studies were conducted in high-income settings. Enrolled patients were reported to have either distant metastatic thyroid cancer or residual disease in about half of the studies. Most studies allowed dietary intake of iodine 50υg/day or less for one to two weeks. Timing of cessation of low-iodine diet was generally by radioactive iodine administration or scanning. Methods of counselling patients were varied (physician counselling, written dietary instructions, use of dietician). None of the included studies assessed long-term recurrence or mortality rates after initial follow-up radioactive iodine scan.
Two reviewers independently selected studies for inclusion; disagreements were resolved through discussions.