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. 2015 Jun;4(2):99-105.
doi: 10.1159/000433426. Epub 2015 Jun 11.

Assessment of the Effect of Two Distinct Restricted Iodine Diet Durations on Urinary Iodine Levels (Collected over 24 h or as a Single-Spot Urinary Sample) and Na(+)/I(-) Symporter Expression

Rosália P Padovani  1 , Rui M B Maciel  2 , Teresa S Kasamatsu  3 , Beatriz C G Freitas  3 , Marilia M S Marone  4 , Cleber P Camacho  2 , Rosa Paula M Biscolla  2
Affiliations

Assessment of the Effect of Two Distinct Restricted Iodine Diet Durations on Urinary Iodine Levels (Collected over 24 h or as a Single-Spot Urinary Sample) and Na(+)/I(-) Symporter Expression

Rosália P Padovani et al. Eur Thyroid J. 2015 Jun.

Abstract

Introduction: A restricted iodine diet (RID) may be recommended for depletion of the whole-body iodine pool in patients with differentiated thyroid cancer referred for radioiodine treatment or a whole-body scan. Evaluation of the iodine pool is possible through urinary iodide (UI) measurements, which can be collected in 24-hour (24U) or spot urinary (sU) samples. However, the minimum period required for an RID to lower the iodine pool, the measurement of iodine in sU samples as a iodine pool marker, and the influence of the iodine pool on Na(+)/I(-) symporter (NIS) expression are debatable in the literature.

Objectives: To compare the effects of 15- and 30-day RID on UI measurements in 24U and sU samples and the impact of RID on NIS expression.

Methods: Thyroidectomized patients went on a 15- or 30-day RID and collected 24U and sU samples before and after the RID. Twenty healthy individuals were evaluated for mRNA NIS expression before and after the RID.

Results: Of 306 patients, only 125 properly complied with both the RID and 24U collection. We observed a correlation between sU and 24U UI before the RID (n = 306, ρ = 0.47, p < 0.001), after a 15-day RID (n = 79, ρ = 0.49, p < 0.001), and after a 30-day RID (n = 46, ρ = 0.73, p < 0.001). There was a significant decrease in UI after the RID. The median UI measurement was 275 μg/l at baseline and 99 and 80 μg/l after a 15- and 30-day RID, respectively. There was a significant increase in NIS expression after a 15-day RID.

Conclusions: A 15-day RID is sufficient to deplete the iodine pool. sU can replace 24U UI as a marker for assessing the iodine pool. NIS expression was increased after a 15-day RID.

Keywords: Na+/I– symporter; Radioiodine therapy; Restricted iodine diet; Thyroid cancer; Urinary iodine.

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Figures

Fig. 1
Fig. 1
UI measurements in 24U and sU samples at baseline (n = 306) (a), after 15 days of RID (n = 79) (d), and after 30 days of RID (n = 46) (g). Correlation between 24U and sU UI samples at baseline (b), after 15 days of RID (e), and after 30 days of RID (h). Bland-Altman plots demonstrating the concordance between 24U and sU UI results at baseline (c), after 15 days of RID (f), and after 30 days of RID (i).
Fig. 2
Fig. 2
a UI measurements at baseline (median 222 μg/l), after 7 days of RID (median 146 μg/l), and after 15 days of RID (median 95 μg/l, p < 0.05) in 20 healthy individuals. b mRNA NIS expression in peripheral blood at baseline (0.83 a.u.), after 7 days of RID (1.58 a.u.), and 15 after days of RID (4.57 a.u., 5.5 times the basal value, p < 0.05) in 20 healthy individuals.
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