A lower thyroid stimulating hormone (TSH) cutoff at the second screening of a 2-screen program for congenital hypothyroidism (CH) can detect additional cases of CH, including infants with thyroid dysgenesis and permanent CH, according to study results published in Journal of Clinical Endocrinology and Metabolism.
Newborn screening for CH has been recommended for many years now, and most screening tests are based on dried blood spot TSH. Over the years, TSH cutoff values have been progressively lowered in many screening programs, and this was suggested to be one of several factors leading to an increased incidence of CH.
Many centers adopted a strategy of repeat screening, which included repeat sampling at 2 weeks. In several screening laboratories, including the Regional Screening Laboratory of Lombardy, the TSH cutoffs at the first (TSH ≥10.0 mU/L) and second (TSH > 5.0 mU/L) screening are different.
The objective of the current study was to characterize infants with CH who were identified by the second screening test, and to compare infants with TSH levels between 5.0 and 9.9 mU/L at the second screening with infants with TSH of 10.0 mU/L or higher at the first screening.
The retrospective study included 119 infants with blood spot TSH elevation on the second newborn screening in the Lombardy region of Italy between 2007 and 2014. Maternal and neonatal clinical features were collected, and infants were divided according to TSH level: 5-9.9 mU/L (low TSH group, 52 infants) and 10 mU/L or higher (high TSH group, 67 infants).
By using a lower TSH cutoff on the second screen, additional cases of CH were detected: In fact, 43.7% of the 119 CH babies included in the study who were identified on second screening would have been missed if the same TSH cutoff of 10.0 mU/L had been used on both screens. Imaging studies showed no significant differences in the frequency of different etiologies of CH between the groups.
There was no different in the frequency of thyroid dysgenesis and eutopic gland or permanent and transient CH between infants in the low TSH group and those in the high TSH group. Similarly, there was no difference between groups in extra-thyroidal malformations or dysmorphic syndromes (21.2% vs 16.4%, respectively) or multiple malformations (7.7% vs 4.5%, respectively).
Regarding neonatal features, preterm birth was more common in the low TSH group (57.7% vs 23.9%; P < .001), mostly due to a higher frequency of infants with gestational age of less than 34 weeks (34.6% vs 6.0%; P < .001). Admission to neonatal intensive care unit was also more common in the low TSH group (50.0% vs 17.9%; P < .001).
As for maternal features, glucocorticoid treatment in pregnancy was more common in mothers of babies in the low TSH group (11.5% vs 1.5%; P = .042). The frequency of maternal hypothyroidism and/or goiter was higher in the low TSH group than in the high TSH group (26.9% vs 10.4%; P = .036).
“This study has demonstrated that a lower TSH cutoff at the second screening can detect additional cases of CH and that a second bTSH cutoff of 5.0 mU/L is appropriate for identifying preterm newborns and babies with associated risk factors,” concluded the researchers.
Caiulo S, Corbetta C, Di Frenna M, et al. Newborn screening for congenital hypothyroidism: the benefit of using differential TSH cutoffs in a two-screen program. Published online Oct 30, 2020. J Clin Endocrinol Metab. doi: 10.1210/clinem/dgaa789