Document Type : Original Article (s)
Authors
1
General Practitioner, Isfahan Endocrine and Metabolic Research Center, Isfahan University of Medical Sciences, Isfahan, Iran
2
Assistant Professor, Department of Statistics and Mathematics, School of Sciences, Persian Gulf University, Bushehr, Iran
3
Associate Professor, Department of Physiology and Pharmacology, School of Medicine, Kashan University of Medical Sciences, Kashan, Iran
4
Professor, Department of Internal Medicine, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran
Abstract
Background: National newborn screening for congenital hypothyroidism (CH) was introduced in Iran in 2005.The Iranian Newborn Screening Program Center recommends a blood spot thyroid stimulating hormone (TSH) cut-off of 5 mlU/L to be used to detect CH. As the value used varies from 5 to 20 mlU/L in the world, we argued the implications of altering this threshold. Methods: In a cross-sectional study during 2006-10, blood spot TSH levels were measured in 3-5 day-old infants. Since the cut-off was 5 mlU/L, infants with TSH > 5 mlU/L were recalled for serum thyroxine (T4) and TSH tests. CH cases were confirmed by having a serum TSH > 5 mlU/L. Findings: Among the 113727 studied infants, 3224 (2.83%) had a first blood spot TSH > 5.0 mlU/L. In addition, 87.69% of the recalled infants had a TSH between 5 and 10 mlU/L. The incidence rate of hypothyroidism in neonates with filter TSH levels of 5-10 mlU/L was 4.67% (132/2827). The 99% confidence interval for the mean value of filter TSH was 16.9-25.1 in patients and 6.2-6.57 in healthy neonates. Conclusion: Regarding the incidence rate of hypothyroidism in neonates with filter TSH values between 5-10 mlU/L and the Newborn Screening Program guidelines which suggest rescreening for the slightly elevated TSH, it seems that repeating the filter test is sufficient, more economic, and less invasive. Besides, raising the threshold to 6.5 mlU/L will reduce a great number of false positive infants while abnormalities of thyroid function requiring treatment will not be missed with a 99% confidence. Keywords: Congenital hypothyroidism, Neonatal screening, Blood spot test
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