Urine iodine concentration in hospitalised infants with thyroid dysfunction

Area of Science:

• Pediatric Endocrinology
• Clinical Chemistry
• Public Health Nutrition

Background:

• Iodine is crucial for thyroid hormone synthesis; imbalances (deficiency or excess) can impair infant thyroid function.
• Urinary iodine concentration (UIC) assesses population iodine status, but a gold standard for individual infant assessment is lacking.
• Thyroid dysfunction in hospitalized infants necessitates reliable diagnostic tools for iodine status.

Purpose of the Study:

• To evaluate the clinical utility of urinary iodine concentration (UIC) in diagnosing thyroid dysfunction in hospitalized infants.
• To investigate the relationship between UIC levels and thyroid hormone status in infants.
• To compare iodine status assessment in infants across different time periods reflecting changes in iodine nutrition policies.

Main Methods:

• Retrospective analysis of hospital records for infants under 24 months with UIC measurements during thyroid dysfunction investigations.
• Inclusion of data from two distinct periods (2007-2009 and 2017-2021) to account for shifts in public health iodine measures.
• Categorization of UIC into deficient (<100 µg/L) and excess (≥300 µg/L) ranges based on WHO criteria.

Main Results:

• 13.8% of infants had UIC in the iodine-deficient range, while 53.9% were in the iodine-excess range.
• The highest UIC quartile (>1432 µg/L) correlated with clinical suspicion of iodine excess, identified exposure sources, prematurity, cardiac anomalies, and surgical history.
• Infants in the highest UIC quartile exhibited significantly lower median free thyroxine (fT4) levels compared to other quartiles (9.4 vs. 12.7 pmol/L).

Conclusions:

• Extremely high random UIC is valuable for confirming suspected iodine excess in hospitalized infants with thyroid dysfunction, particularly during critical illness.
• Free thyroxine (fT4) levels appear to be a more sensitive indicator of thyroid dysfunction severity than TSH elevation in critically ill, often premature infants with high UIC.
• UIC measurement, interpreted within clinical context, aids in managing iodine-related thyroid dysfunction in complex pediatric cases.