<prompt> The most sensitive indicator of Environmental iodine deficiency is:-Serum T4 levelsSerum T3 levelsUrine iodine excretionNeonatal hypothyroidism  <response>: Neonatal hypothyroidism is the most sensitive indicator of environmental iodine deficiency. Other useful indicators for assessment of Iodine deficiency: Prevalence of goiter Prevalence of cretinism Urinary iodine excretion Major impact indicator Measurement of thyroid function by determination of serum T4, TSH. 