Iodine exposure and thyroid function in premature infants - Tips from Other Journals

Author: Grace Brooke Huffman
Date: Feb 15, 1997

Premature infants are known to have low levels of thyroxine ([T.sub.4]), triiodothyronine ([T.sub.3]) and thyrotropin (TSH). Disorders of the thyroid may subsequently develop in infants who are exposed to high levels of iodine. Parravicini and colleagues evaluated the effect of iodine exposure on thyroid function in very-low-birth-weight neonates.

Forty-four very-low-birth-weight infants (less than 1,500 g [3 lb, 5 oz]) were grouped by levels of postnatal iodine exposure. Urine samples were collected several times from each infant to test the level of iodine uptake from various antiseptic solutions and/or contrast material used in these infants. Thyroid function tests were also measured in each infant.

The control group included 18 small-for-gestational-age infants never exposed to iodine. An antiseptic solution of 10 percent povidone-iodine was used in nine infants at the site of invasive procedures, such as venipuncture or intravenous line placement. Twelve infants received an injection of an iodine-containing contrast medium. Five infants were exposed to both the antiseptic solution and the contrast medium. A group of average-weight infants served as a comparison group.

The levels of iodine in the urine of the infants exposed to povidone-iodine and the contrast medium were significantly higher than the levels in the control group. By two weeks after birth, no significant differences were apparent between the four groups of infants. The infants exposed to increased iodine also had significantly higher TSH levels than the unexposed infants. In addition, the mean levels of TSH for both the study infants and the average weight infants who were exposed to iodine were much higher than for infants who were not exposed, regardless of birth weight. Between two and four weeks of age, however, the small-for-gestational-age infants continued to have higher levels of TSH when compared with exposed average-weight infants of the same age.

The authors conclude that premature infants tend to have a large uptake of iodine from sources that may be considered routine for some medical procedures. Of particular concern is the fact that this uptake of iodine is associated with significant changes in thyroid function. They recommend avoiding iodine-containing compounds (such as the commonly used povidone-iodine solution) in very-low-birth-weight infants whenever possible.

Parravicini E, et al. Iodine, thyroid function, and very low birth weight infants. Pediatrics 1996;98:730-4.

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