Abstract
Low-iodine diet (LID) is a crucial preparation for radioactive iodine (RAI) treatment or scan in thyroid cancer. The aim of this study is to analyze the influence of thyroid stimulating hormone (TSH) stimulation protocols and other clinical factors on LID adequacy. Thyroid cancer patients who underwent LID for RAI scan or treatment were retrospectively analyzed. Patients were guided to have LID for 2 weeks before RAI administration and urine iodine/creatinine ratio (UICR, μg/g Cr) was measured. TSH stimulation was conducted using either thyroid hormone withdrawal (THW) or recombinant human TSH (rhTSH) injection. Adequacy of LID was classified by UICR as 'excellent (< 50)', 'adequate (50-100)', 'inadequate (101-250)' and 'poor (> 250)'. A total of 1715 UICR measurements from 1054 patients were analyzed. UICR was significantly higher in case of rhTSH use than THW (72.4 ± 48.1 vs. 29.9 ± 45.8 μg/g Cr, P < 0.001). In patients who underwent LID twice using both TSH stimulation protocols alternately, UICR was higher in case of rhTSH than THW regardless of the order of method. Among clinical factors, female, old-age, and the first LID were significant factors to show higher UICR. Although the adequacy of LID was 'adequate' or 'excellent' in most patients, multivariate analysis demonstrated that THW method, male, young age, and prior LID-experience were significant determinants for achieving 'excellent' adequacy of LID. In conclusion, UICR was higher and the proportion of 'excellent' LID adequacy was lower with rhTSH than with THW. UICR was higher also in women, old-age, and LID-naïve patients. Further researches are required to suggest effective methods to reduce body iodine pool in case of rhTSH use and to validate the efficacy of such methods on outcomes of RAI treatment.
Highlights
In differentiated thyroid cancer, radioactive iodine (RAI) treatment and scan are crucial therapeutic and diagnostic modalities
thyroid stimulating hormone (TSH) stimulation is conducted by thyroid hormone withdrawal (THW) or recombinant human TSH injection
The aim of the present study is to evaluate the influence of the different TSH stimulation protocols on the adequacy of low-iodine diet (LID)
Summary
Radioactive iodine (RAI) treatment and scan are crucial therapeutic and diagnostic modalities. RAI scan or treatment requires two kinds of patient preparations; thyroid stimulating hormone (TSH) stimulation and low-iodine diet (LID) [3,4]. TSH stimulation is conducted by thyroid hormone withdrawal (THW) or recombinant human TSH (rhTSH) injection. LID reduces body iodine pool, which is deemed to enhance RAI uptake by thyroid or cancer cells. Despite some debates on the effect of LID, most guidelines on thyroid cancer recommend LID to restrict iodine intake < 50 μg/day, for 1–2 weeks before RAI administration. In case of rhTSH use without THW, metabolized thyroid hormone may be a potential source that increases body iodine pool because iodine is the major component of synthetic thyroid hormones (approximately 64% of levothyroxine and 57% of liothyronine)
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