Specific tissues in the body require adequate iodine and the reduced form of the element, iodide, for normal metabolism and optimal health. Adequate iodide uptake and organification of iodine by the thyroid gland is required for the production, storage and release of thyroid hormones. Triiodothyronine (T3) regulates metabolism in several tissues by affecting energy production and neuronal and sexual development. Iodine insufficiency is associated with "sub-clinical" thyroid deficiency, weight gain, loss of energy, goitre and impaired mental function. Iodine is also concentrated in breast tissue where it elicits anti-proliferative effects and protection against fibrocystic breast disease and cancer. Iodine and organic iodine compounds are also concentrated and secreted by the gastric mucosa, salivary glands and the cervix. The test requires a spot urine specimen, preferably first morning void (FMV), for determination of baseline halide levels. An oral loading dose of iodine/iodide is ingested and all urine is collected for the subsequent 24 hours. Iodine is measured in the urine and the results for each element are reported as µg/gm creatinine and µg/24 hours. Iodine status is assessed by evaluation of the percentage of the ingested dose that is excreted. Low iodine excretion is suggestive of greater bodily retention and need.