Use of Salivary Iodine Concentrations to Estimate the Iodine Status of Adults in Clinical Practice

Background: Measurement of the 24-h urinary iodine concentration or urinary iodine excretion (UIE) is the gold standard to determine iodine status; however, this method is inconvenient. The use of salivary iodine could be a possible alternative since salivary glands express the sodium-iodine symporter.Objectives: We aimed to establish the correlation between the salivary iodine secretion and UIE, to evaluate the clinical applicability of the iodine saliva measurement.Methods: We collected 24-h urine and saliva samples from 40 participants >= 18 y: 20 healthy volunteers with no specific diet (group 1), 10 patients with differentiated thyroid cancer with a low dietary intake (<50 mu g/d, group 2), and 10 patients with a high iodine status as the result of the use of amiodarone (group 3). Urinary and salivary iodine were measured using a validated inductively coupled plasma MS method. To correct for differences in water content, the salivary iodine concentration (SIC) was corrected for salivary protein and urea concentrations (SI/SP and SI/SU, respectively). The intra-and inter-individual CVs were calculated, and the Kruskal-Wallis test and Spearman's correlation were used.Results: The intra-individual CVs for SIC, SI/SP and SI/SU were 63.8%, 37.7%, and 26.9%, respectively. The inter-individual CVs for SIC, SI/SP and SI/SU were 775%, 41.6% and 470%, respectively. We found significant differences (P < 0.01) in urinary and salivary iodine concentrations between all groups [the 24-h UIE values were 176 mu g/d (IQR, 96.1-213 mu g/d), 26.0 mu g/d (IQR, 22.0-37.0 mu g/d), and 10.0*10(3) mu g/d (IQR, 757*10(3)-11.4*10(3) mu g/d) in groups 1-3, respectively; the SIC values were 136 mu g/L (IQR, 86.3-308 mu g/L), 71.5 tg/L (IQR, 29.5-94.5 mu g/L), and 14.3*10(3) mu g/L (IQR, 10.6*10(3) 25.6*10(3) mu g/L) in groups 1-3, respectively]. Correlations between the 24-h UIE and SIC, sysp and SI/SU values were strong (rho = 0.80, rho = 0.90, and rho = 0.86, respectively; P < 0.01).Conclusions: Strong correlations were found between salivary and urinary iodine in adults with different daily iodine intakes. A salivary iodine measurement can be performed to assess the total iodine body pool, with the recommendation to correct for salivary protein or urea.