The limitations of thyroid volume reference values in assessment of iodine nutrition after recent introduction of iodine prophylaxis
Malgorzata Trofimiuk1, Monika Buziak-Bereza1, Zbigniew Szybinski1, Andrzej Lewinski2, Arkadiusz Zygmunt2, Filip Golkowski1, Jerzy Sowinski3, Bohdana Dorant4, Elzbieta Bandurska-Stankiewicz5, Jerzy Naskalski6, Witold Rostworowski6 & Alicja Hubalewska-Dydejczyk1
Goiter frequency (GF) in schoolchildren and urinary iodine concentration (UIC) in an appropriately large population sample are iodine nutrition (IN) best indicators. GF in mildly iodine deficient areas should be assessed ultrasonographically, as palpation sensitivity in such cases is low.
Aim: To assess thyroid volume reference values as IN marker in population with recently introduced obligatory iodine prophylaxis (OIP).
Material and methods: Data from 7489 schoolchildren aged 612 years examined between 1999 and 2009 were analyzed. 36.33% of children were born after OIP implementation. Thyroid volume was assessed ultrasonographically according to standard procedures. Reference values by Delange et al. (DRV) and Zimmermann et al. (ZRV) were used for GF calculation. UIC was assessed in casual morning sample using Sandell-Kolthoff method.
Results: Median UIC value in study sample was 92.29 μg/l (mean 106.39±68.76 μg/l), 54.05% of children excreted <100 μg/l. GF was 4.23 and 51.14% according to DRV and ZRV, respectively. There was no statistically significant difference in GF according to DRV between children with UIC less and more than 100 μg/l (4.42 vs 4.0%), whereas GF was significantly lower (P=0.01) with UIC>100 μg/l when ZRV were applied (52.42% vs. 49.85%). GF in children born after 1996 was significantly lower according to DRV and higher according to ZRV (1.95 vs 5.54% for born before 1997, P=0.00 and 53.40 vs 49.85%, P=0.03; respectively). GF in children aged 1012 years was higher than in younger ones (DRV: 5.32 vs 3.31%, P=0.00; ZRV: 52.48 vs 50.0%, P=0.03; respectively).
Conclusions: Although UIC indicates that Poland is area of borderline iodine sufficiency, ZRV overrate GF in schoolchildren. Previously recommended DRV dont mirror all trends in GF resulting from improved IN (children born after OIP implementation were younger). Establishing of the separate reference values for mildly insufficient and recently iodine sufficient populations seems to be reasonable.