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.