Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1028 page)

   Iodine is an essential component of T
₄
and T
₃
, and it must be provided in the diet. Inadequate iodine intake leads to inadequate thyroid hormone production, and all the consequences of iodine deficiency stem from the associated hypothyroidism. However, iodide excess can also cause thyroid dysfunction. Goiter is the most obvious manifestation of iodine deficiency. Low iodine intake leads to reduced T
₄
and T
₃
production, which results in increased thyrotropin (TSH) secretion in an attempt to restore T
₄
and T
₃
production to normal.

   
Normal range:

   International groups recommend the following median urinary iodine concentration as the best single indicator of iodine nutrition in populations:

   Severe deficiency: 0–0.15 μmol/L (0–19 μg/L)

   Moderate deficiency: 0.16–0.38 μmol/L (20–49 μg/L)

   Mild deficiency: 0.40–0.78 μmol/L (50–99 μg/L)

   Optimal iodine nutrition: 0.79–1.56 μmol/L (100–199 μg/L)

   More than adequate iodine intake: 1.57–2.36 μmol/L (200–299 μg/L)

   Excessive iodine intake: 2.37 μmol/L (300 μg/L)

   The range in which the median falls is more important than the precise number.

   Use

   Diagnosis of transient thyroid dysfunction and iodine-induced hyperthyrosis

   Biochemical indicator for the assessment of iodine status