Abstract
Back ground: Iodine deficiency is one of the important factors in increasing the recall rate in congenital hypothyroidism (CH) screening programs. The present study assessed whether the iodine status of the general population may predict the recall rate or vice versa. Methods: In the current national study, among 1,382,229 live births delivered between March 2010 and March 2011, 1,288,237 neonates were screened for detecting CH by TSH (thyroid stimulating hormone) measurement via heel prick sampling. Simultaneously, a total of 11,280 school-aged children, aged 7–8 years, were selected using random multi-cluster sampling for measurement of urinary iodine. Results: A negative correlation was found between median urinary iodine (MUI) and the recall rate (r = −0.33, p = 0.03). No correlation was found between MUIC (median urinary iodine concentration) and the incidence rate of CH. Linear regression analysis showed a 0.1% increase in the recall rate for a one unit decrease in MUIC (β = −0.11, 95% CI: −0.2, −0.1, p = 0.03). MUIC, at a cut-off point of 144.7 µg/L, was predictive for a recall rate < 3% (p = 0.05). Conclusion: Frequencies of TSH ≥ 5 mU/L may be a more sensitive indicator for iodine status during pregnancy rather than in the general population. As higher recall rates reflect inadequate iodine nutrition, sufficient iodine supplementation is needed to reduce the recall rate in such communities.
Highlights
Iodine is an essential micronutrient for thyroid hormone synthesis [1]
Neonates with a Guthrie thyroid stimulating hormone (TSH) test ≥ 5 mU/L, were recalled for confirmatory tests and the final diagnosis was made by a pediatric endocrinologist, appointed as the focal point of the congenital hypothyroidism (CH) program in each university region
On a national level, screening revealed TSH < 5, 5–9, 10–19.9 and ≥20 mU/L in 97.2, 2.6, 0.2, and 0.0% of neonates, respectively; as shown, recall rates range from 0.2% to 6.0%
Summary
Iodine is an essential micronutrient for thyroid hormone synthesis [1]. Adequate iodine intake is required to sustain normal thyroid function and body metabolism, especially in pregnancy, during which maternal iodine requirements are increased due to increased thyroid hormone production, iodine transfer to the fetus (iodine in early pregnancy and thyroid hormones in later pregnancy), and increased urinary iodine loss [2]. Iodine deficiency is one of the important factors in the increasing recall rate (the percentage of screening tests with elevated TSH) and the incidence of transient congenital hypothyroidism and infants born in iodine depleted areas tend to have higher thyroid stimulating hormone (TSH). Based on the World Health Organization (WHO) recommendation, the frequency of neonatal TSH > 5 mU/L in whole blood of 40.0% indicate mild, moderate, and severe iodine deficiency, respectively [6]. In Iran and some parts of the world [8,9,10], since the TSH cut off in the national screening program for congenital hypothyroidism has been set at 5 mU/L, frequencies of TSH values > 5 mU/L yield the recall rate in these areas
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