Newborn Screening in the US May Miss Mild Persistent Hypothyroidism.

OBJECTIVE: To determine if newborn screening (NBS) programs for congenital hypothyroidism in the US use thyroid-stimulating hormone (TSH) cutoffs that are age adjusted to account for the physiologic 4-fold reduction in TSH concentrations over the first few days of life. STUDY DESIGN: All NBS programs in the US were contacted and asked to provide information on their NBS protocols, TSH cutoffs, and whether these cutoffs were age adjusted. RESULTS: Of 51 NBS programs, 28 request a repeat specimen if the initial eluted serum TSH concentration is mildly increased (between the cutoff and a median upper limit of 50 mU/L), whereas 14 programs perform a routine second screen in all infants. Although these specimens are typically collected between 1 week and 1 month of life, 16 of the 28 programs with a discretionary second test and 8 of 14 programs with a routine second test do not have age-adjusted TSH cutoffs after the first 48 hours of life. CONCLUSIONS: There is variation in NBS practices for screening for congenital hypothyroidism across the US, and many programs do not adjust the TSH cutoff beyond the first 2 days of life. Samples are processed when received from older infants, often to retest borderline initial results. This approach will miss congenital hypothyroidism in infants with persistent mild TSH elevations. We recommend that all NBS programs provide age-adjusted TSH cutoffs, and suggest developing a standard approach to screening for congenital hypothyroidism in the US.

Congenital hypothyroidism caused by excess prenatal maternal iodine ingestion.

We report the cases of 3 infants with congenital hypothyroidism detected with the use of our newborn screening program, with evidence supporting excess maternal iodine ingestion (12.5 mg/d) as the etiology. Levels of whole blood iodine extracted from their newborn screening specimens were 10 times above mean control levels. Excess iodine ingestion from nutritional supplements is often unrecognized.

Follow-up of newborns with elevated screening T4 concentrations.

OBJECTIVE: To determine the type and incidence of hyperthyroxinemic disorders detected by follow-up of infants with elevated screening total T4 (TT4) values. STUDY DESIGN: Infants born in Oregon with a screening TT4 measurement >3 SD above the mean were offered enrollment. Serum TT4, free T4, total T3, free T3, and thyroid-stimulating hormone concentrations were measured in study infants and their mothers. RESULTS: Over a 20-month period, 101 infants (51 boys) and their mothers enrolled in the study (of 241 eligible infants), from a total screening population of 80,884; 17 infants were identified with persistent hyperthyroxinemia (TT4 >16 microg/dL). Ten had thyroxine-binding globulin excess (1:8088), 5 had evidence for increased T4 binding but not thyroxine-binding globulin excess (1:16,177), and 2 had findings compatible with thyroid hormone resistance (1:40,442); the other 84 infants had transient hyperthyroxinemia. Sequence analysis revealed a point mutation in the thyroid hormone receptor-beta gene in one infant with thyroid hormone resistance; no mutation was identified in the other infant. CONCLUSIONS: Although neonatal Graves' disease occurs in approximately 1 in 25,000 newborn infants, we did not detect any case among 80,884 infants, most likely because their mothers were receiving antithyroid drugs. Although the other hyperthyroxinemic disorders in the aggregate occur frequently (1:4758) and may benefit from detection, in general they do not require treatment.

Initial treatment dose of L-thyroxine in congenital hypothyroidism.

OBJECTIVES: To determine the optimal initial treatment dose of L-thyroxine in congenital hypothyroidism (CH) by evaluating the time course of rise of thyroxine (T(4)) and free T(4) concentrations into an established "target range" and normalization of thyroid-stimulating hormone (TSH) and to reevaluate the "target range" for T(4) and free T(4) concentrations during the first 2 weeks of CH treatment. STUDY DESIGN: Infants of birth weight 3 to 4 kg with CH (n = 47) detected by newborn screening were randomly assigned into three L-thyroxine treatment dose arms: 37.5 microg/day (group 1); 62.5 microg/day for 3 days, then 37.5 microg/day (group 2); and 50 microg/day (group 3). Serum T(4), free T(4), triiodothyronine (T(3)), free T(3), and TSH were measured before treatment and at 3 days and 1, 2, 4, 8, and 12 weeks after treatment. RESULTS: T(4) and free T(4) concentrations increased into the target range (10 to 16 microg/dL) by 3 days of therapy in infants in groups 2 and 3 and by 1 week in group 1; 50 microg/day (average 14.5 microg/kg/day) provided the most rapid normalization of TSH by 2 weeks. With the use of linear regression analysis of T(4) versus TSH or free T(4) versus TSH plots, the intercept at the lower range of normal for TSH (1.7 mU/L) showed T(4) = 19.5 microg/dL and free T(4) = 5.23 ng/dL. CONCLUSIONS: Initial dosing of 50 microg/day (12-17 microg/kg per day) raised serum T(4) and free T(4) concentrations to target range by 3 days and normalized TSH by 2 weeks of therapy. We recommend consideration of a somewhat higher "target range" of 10 to 18 microg/dL for T(4) and 2 to 5.0 ng/dL for free T(4) during the first 2 weeks of L-thyroxine treatment. After 2 weeks of treatment, the target range drops to 10 to 16 microg/dL for T(4) and 1.6 to 2.2 for free T(4).