Transient Versus Permanent Congenital Hypothyroidism in Ontario, Canada: Predictive Factors and Scoring System.

CONTEXT The apparent increased incidence of congenital hypothyroidism (CH) is partly due to increased detection of transient disease. OBJECTIVE To identify predictors of transient CH (T-CH) and establish a predictive tool for its earlier differentiation from permanent CH (P-CH). DESIGN Retrospective cohort study of patients diagnosed with CH from 2006-2015 through Newborn Screening Ontario (NSO). RESULTS Of 469 cases, 360 (76.8%) were diagnosed with P-CH vs. 109 (23.2%) with T-CH. Doses of levothyroxine predicting T-CH were <3.9 mcg/kg at 6 months, <3.0 mcg/kg at 1 and 2 years, and <2.5 mcg/kg at 3 years. Descriptive statistics and multivariable logistic modeling demonstrated several diverging key measures between patients with T-CH versus P-CH, with optimal stratification at 1-year of age. Thyroid imaging was the strongest predictor (p<0.001). Excluding imaging, significant predictors in the first year of life included thyroxine dose/kg (p<0.001-0.002), rise in TSH above the reference interval during treatment (p=0.002), screening TSH (p=0.03), and a history of maternal thyroid disease (p=0.02). Based on the 1-year model without imaging, a risk score was developed to identify children with T-CH who may benefit from an earlier trial off therapy, to reduce excess medicalization and healthcare costs. CONCLUSION A levothyroxine dose of <3 mcg/kg at 1 and 2 years of age and <2.5 mcg/kg at 3 years of age can be predictive of T-CH. A novel risk score was developed that can be clinically applied to predict the likelihood of a successful trial off therapy for a given patient at 1 year of age.