From the Guidelines
The primary purpose of the urinary iodine test is to assess iodine status by measuring the amount of iodine excreted in urine, which is essential for evaluating thyroid function and metabolism. This test is crucial in determining whether an individual has adequate iodine levels, as iodine deficiency can lead to conditions such as goiter, hypothyroidism, and impaired cognitive development in children, while excess iodine can cause thyroid dysfunction in susceptible individuals 1. The test involves collecting a urine sample, either as a spot sample or a 24-hour collection, which is then analyzed for iodine concentration. According to the espen micronutrient guideline published in Clinical Nutrition in 2022, iodine status shall be assessed by urinary 24 h excretion, combined with assessment of thyroid function and size, with a strong consensus of 94% 1.
The urinary iodine test is used in various clinical scenarios, including:
- Evaluating thyroid disorders
- Assessing nutritional status in populations at risk for iodine deficiency
- Monitoring iodine supplementation effectiveness The test results are typically reported in micrograms per liter (μg/L) or micrograms per 24 hours, with normal ranges varying by age, sex, and pregnancy status 1. It is worth noting that serum TSH is not a sensitive indicator of iodine status, and therefore, urinary iodine excretion is considered a more reliable marker of iodine status 1.
In terms of reference values, the espen micronutrient guideline suggests that serum iodine levels should be between 40-100 mg/L, while urine iodine levels should be between 100-300 mg/24hr 1. Overall, the urinary iodine test is a valuable tool in assessing iodine status and guiding clinical decision-making to prevent and manage iodine-related disorders.
From the Research
Purpose of Urinary Iodine Test
The urinary iodine test is used to assess iodine intake and deficiency in individuals.
- It measures the amount of iodine excreted in the urine, which reflects the total iodine intake from all sources 2.
- The test is essential in identifying populations with excessive or deficient iodine intakes, which can lead to various thyroid disorders 2, 3.
- Iodine deficiency can cause goiter, hypothyroidism, cretinism, and impaired cognitive development, while excess iodine intake can precipitate hyperthyroidism, hypothyroidism, goiter, and/or thyroid autoimmunity 4, 2, 5.
Clinical Implications
The urinary iodine test has significant clinical implications, particularly in:
- Pregnant or lactating women, who require adequate iodine intake for fetal neurodevelopment and thyroid hormone synthesis 4, 5.
- Individuals with preexisting thyroid disease or those previously exposed to iodine deficiency, who may be more susceptible to thyroid disorders due to changes in iodine intake 2.
- Populations with limited access to iodized salt, dairy products, or other iodine-rich foods, who may be at risk of iodine deficiency 4, 5.
Assessment and Interpretation
The urinary iodine test can be used in conjunction with other biomarkers, such as thyroglobulin, to assess iodine intake and thyroid function 2.
- The median urinary iodine concentration (UIC) of a population reflects the total iodine intake from all sources and can accurately identify populations with excessive iodine intakes 2.
- Creatinine adjustment may be necessary to account for variations in urine concentration and ensure accurate interpretation of urinary iodine measurements 6.