Predictive factors of permanent versus transient congenital hypothyroidism. A pragmatic cohort study.

Purpose: To investigate potential predictors that may be used in clinical practice to discriminate between permanent congenital hypothyroidism (PCH) and transient congenital hypothyroidism (TCH).

Methods: A retrospective cohort study was conducted, enrolling neonates diagnosed with congenital hypothyroidism (CH) by neonatal screening test or blood testing due to risk factors. The levothyroxine (LT4) dose and thyroid stimulating hormone (TSH) levels of children from birth to three years of age were recorded.

Results: 88 neonates were enrolled, 35 with PCH and 53 with TCH. Doses above 3.8μg/kg/d at 6 months (sensitivity:62%, specificity:96%), 3.0μg/kg/d at 12 months (sensitivity:64%, specificity:97%), 2.6μg/kg/d at 2 years (sensitivity:80%, specificity:98%), and 2.5μg/kg/d at 3 years (sensitivity:89%, specificity:98%) of age could predict PCH. The need for a daily total LT4 dose>50µg at any time of the follow-up period was observed solely in the PCH group (28% vs 0% p<0.0001). Independent predictors of discrimination between PCH and TCH were TSH levels at diagnosis (beta=-4.3, p<0.001), the daily dose of LT4 at six months (beta=-2.9, p=0.004), at 12 months (beta=-3.4, p=0.0007), and at 24 months of age (beta=-3.2, p=0.0013), TSH>5μIU/ml at any time after treatment initiation (beta:-3.6, p=0.0003), and the need for LT4 dose increase more than twice (beta:-3.2, p=0.0009). Conclusions: To discriminate PCH from TCH in this study, LT4 dosing, and a combination of prognostic markers such as total LT4>50µg along with TSH levels at diagnosis, the need to increase the LT4 dose during treatment and TSH levels>5μIU/mL at any time during the treatment period could be used.