Abstract
Lower cutoff levels in screening programs have led to an increase in the proportion of detected cases of transient hypothyroidism, leading to an increase in the overall prevalence of primary congenital hypothyroidism (CH) in several countries. We have performed a retrospective evaluation on the data from 251,008 (96.72%) neonates screened for thyroid-stimulating hormone (TSH) level in dried blood spot specimens taken 48 h after birth, between 2002 and 2015, using the DELFIA method. A TSH value of 15 mIU/L whole blood was used as the cutoff point until 2010 and 10 mIU/L thereafter. Primary CH was detected in 127 newborns (1/1976) of which 81.1% had permanent and 18.9% had transient CH. The prevalence of primary CH increased from 1/2489 before 2010 to 1/1585 thereafter (p = 0.131). However, the prevalence of permanent CH increased only slightly (p = 0.922), while the transient CH prevalence showed an 8-fold increase after lowering the TSH cutoff level (p < 0.001). In cases of permanent CH, we observed a lower prevalence of thyroid dysgenesis (82.7% vs. 66.7%) and a higher prevalence of a normal in situ thyroid gland (17.3% vs. 33.3%), for the period with a lower TSH cutoff value. Our findings support the impact of a lower TSH cutoff on the increasing prevalence of congenital hypothyroidism.
Highlights
A reliable primary congenital hypothyroidism (CH) prevalence of 1/3000–1/4000 was reported when neonatal screening for CH was first introduced [1]
Lower thyroid-stimulating hormone (TSH) cutoffs have been adopted in some neonatal thyroid screening programs worldwide, leading to a progressive increase in the detection of additional mild forms of the disease and with that an increase in the overall prevalence of CH [3,7]
The higher prevalence of CH was observed over period 2, indicating the impact of lowering the TSH cutoff level on the overall CH prevalence
Summary
A reliable primary congenital hypothyroidism (CH) prevalence of 1/3000–1/4000 was reported when neonatal screening for CH was first introduced [1]. Potential causes include environmental factors, changes in the ethnic composition of the population, modification of the screening program methodology and application of the lower thyroid-stimulating hormone (TSH) cutoff level at screening [5,6,7,8]. The shift from primary T4 to primary TSH screening strategies, and the lowering of the TSH cutoff levels have been attributed to the increasing CH prevalence worldwide, probably due to more frequent detection of the milder forms of CH. The majority of cases detected using a lower TSH cutoff tend to have milder hypothyroidism, with imaging often demonstrating an eutopic, “gland in situ”. Some cases turn out to have transient CH [5,7,9,10,11]
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