Newborn Screening for Congenital Hypothyroidism: Recommended Guidelines

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Abstract
During the past decade newborn screening for congenital hypothyroidism has become an important health activity in most developed countries. These screening programs have not only benefited patients and their families but also have produced new information about the epidemiology, pathophysiology, diagnosis, and treatment of thyroid disease in infancy and childhood. During this period of implementation and growth of the screening programs, a variety of issues and questions arose. Some of these have been resolved, and some have not. The point has now been reached where collation of the combined experiences of the North American programs can address these issues. The reader should understand that what follows reflects current opinion and may require changes when the results of the next decade of screening are reviewed. SCREENING METHOD Thyroxine (T4) and Thyroid-Stimulating Hormone (TSH) Most North American programs use a two-tiered laboratory approach. An initial T4 measurement is followed by measurement of TSH in specimens with low T4 values. In addition to detecting infants with primary hypothyroidism (low or low normal T4 level with elevated TSH value; prevalence 1:3,500 to 4,500 newborns), this approach can also identify infants with thyroxine-binding globulin deficiency and some with hypothalamic-pituitary hypothyroidism (low or low normal T4 level with normal TSH value; prevalence 1:5,000 to 10,000 and 1:50,000 to 150,000 newborns, respectively). Programs that quantify T4 values also have the option of identifying newborns with hyperthyroxinemia (1:20,000 to 40,000 newborns). On the other hand, this approach will miss infants who have normal T4 values but elevated TSH values. Such infants are relatively commonplace in European programs where initial screening is done by measurement of TSH.

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