A systematic review of thyroid dysfunction in preterm neonates exposed to topical iodine.

OBJECTIVE: To determine whether maternal exposure to iodine or neonatal exposure to topical iodine-containing solutions increases the risk of transient thyroid dysfunction in neonates born <32 weeks' gestation or <1.5 kg. DESIGN: Systematic review. SEARCH STRATEGY: Electronic searches were conducted using Medline and the Cochrane Library. ELIGIBILITY CRITERIA: A study was eligible for review if it reported neonatal exposure to topical iodine or maternal iodine exposure. The key outcome measure was neonatal thyroid function. The search had no restrictions on date of publication, type of study or language. RESULTS: 794 papers were identified during the initial search; 15 studies were fully reviewed. The incidence of (transient) hypothyroidism/hyperthyrotropinaemia following exposure to topical iodine ranged from 12 to 33 per 100 infants; the incidence in non-exposed infants was 0. CONCLUSIONS: There is evidence that neonatal exposure to iodine-containing disinfectants causes thyroid dysfunction in infants born <32 weeks. None of the studies evaluated neurodevelopment. Larger scale studies are needed to determine definitively the nature of the relationship and the impact of exposure on neurodevelopment. In the meantime, it would seem prudent to restrict exposure of iodine-containing skin disinfectants in preterm infants; chlorhexidine might be a credible alternative.

One month is sufficient for urinary iodine to return to its baseline value after the use of water-soluble iodinated contrast agents in post-thyroidectomy patients requiring radioiodine therapy.

BACKGROUND: There is a concern regarding the use of iodinated contrast agents (ICA) for chest and neck computed tomography (CT) to localize metastatases in patients with differentiated thyroid cancer (DTC). This is because the iodine in ICA can compete with (131)I and interfere with subsequent whole scans or radioactive iodine treatment. The required period for patients to eliminate the excess iodine is not clear. Therefore, knowing the period for iodine levels to return to baseline after the injection of ICA would permit a more reliable indication of CT for DTC patients. The most widely used marker to assess the plasmatic iodine pool is the urinary iodine (UI) concentration, which can be collected over a period of 24 hours (24U) or as a single-spot urinary sample (sU). As 24U collections are more difficult to perform, sU samples are preferable. It has not been established, however, if the measurement of iodine in sU is accurate for situations of excess iodine. METHODS: We evaluated 25 patients with DTC who received ICA to perform chest or neck CT. They collected 24U and sU urinary samples before the CT scan and 1 week and 1, 2, and 3 months after the test. UI was quantified by a semiautomated colorimetric method. RESULTS: Baseline median UI levels were 21.8 µg/dL for 24U and 26 µg/dL for sU. One week after ICA, UI median levels were very high for all patients, 800 µg/dL. One month after ICA, however, UI median levels returned to baseline in all patients, 19.0 µg/dL for 24U and 20 µg/dL for sU. Although the values of median UI obtained from sU and 24U samples were signicantly different, we observed a significant correlation between samples collected in 24U and sU in all evaluated periods. CONCLUSION: One month is required for UI to return to its baseline value after the use of ICA and for patients (after total thyroidectomy and radioiodine therapy) to eliminate the excess of iodine. In addition, sU samples, although not statistically similar to 24U values, can be used as a good marker to evaluate patients suspected of contamination with iodine.