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.
BACKGROUND
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.


OBJECTIVE
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.
Thyroid Diseases Center and Laboratory of Molecular and Translational Endocrinology, Division of Endocrinology, Department of Medicine, Escola Paulista de Medicina, Universidade Federal de São Paulo, Brazil ; Thyroid Diseases Center, Instituto Israelita de Ensino e Pesquisa Albert Einstein, São Paulo, Brazil ; Department of Nuclear Medicine, Irmandade Santa Casa de Misericórdia de São Paulo, São Paulo, Brazil.
Rosália P
RP
Padovani
Thyroid Diseases Center and Laboratory of Molecular and Translational Endocrinology, Division of Endocrinology, Department of Medicine, Escola Paulista de Medicina, Universidade Federal de São Paulo, Brazil ; Thyroid Diseases Center, Instituto Israelita de Ensino e Pesquisa Albert Einstein, São Paulo, Brazil.
Rui M B
RM
Maciel
Thyroid Diseases Center and Laboratory of Molecular and Translational Endocrinology, Division of Endocrinology, Department of Medicine, Escola Paulista de Medicina, Universidade Federal de São Paulo, Brazil.
Teresa S
TS
Kasamatsu
Thyroid Diseases Center and Laboratory of Molecular and Translational Endocrinology, Division of Endocrinology, Department of Medicine, Escola Paulista de Medicina, Universidade Federal de São Paulo, Brazil.
Beatriz C G
BC
Freitas
Department of Nuclear Medicine, Irmandade Santa Casa de Misericórdia de São Paulo, São Paulo, Brazil.
Marilia M S
MM
Marone
Thyroid Diseases Center and Laboratory of Molecular and Translational Endocrinology, Division of Endocrinology, Department of Medicine, Escola Paulista de Medicina, Universidade Federal de São Paulo, Brazil ; Thyroid Diseases Center, Instituto Israelita de Ensino e Pesquisa Albert Einstein, São Paulo, Brazil.
Cleber P
CP
Camacho
Thyroid Diseases Center and Laboratory of Molecular and Translational Endocrinology, Division of Endocrinology, Department of Medicine, Escola Paulista de Medicina, Universidade Federal de São Paulo, Brazil ; Thyroid Diseases Center, Instituto Israelita de Ensino e Pesquisa Albert Einstein, São Paulo, Brazil.
Rosa Paula M
RP
Biscolla
Na+/I– symporter; Radioiodine therapy; Restricted iodine diet; Thyroid cancer; Urinary iodine